Breaking down doors is loud, doors have uses, and some doors are much harder to break down than others.

Breaking down doors is loud. Unlike picking a lock, smashing a lock is a loud and attention attracting activity. Monsters can pinpoint your player's location and prepare an ambush, flee with treasure, and generally do a lot of unpleasant things. Enemies can find the broken door and track you down. If there's no monsters close by then, have at it. No consequences, no time pressure, let them succeed.

Doors have uses. They stop people entering places. If you leave a door intact you can use it to bar enemies, you can use it to lock someone in places, you can use it to be more stealthy. There are often good reasons to leave barriers intact. Picking a lock gives you control over that lock, in that there is still a door to be locked or barred. Likewise, chests have uses, they keep items safe- if you smash them, those items are not gonna be happy.

Some doors are much harder to break down than others. Some doors have heavy bars on them, or are made of iron or steel or magical materials. Some are giant stone columns that only open if you say friend in elvish. For these doors the lock picking roll might be much lower than the breaking roll, so it will be much faster and actually feasible to pick the lock than smash it.

If there is no downside to breaking down a door compared to unlocking it, there is no point in choosing one over the other (except for ability to do either)

Unlocking a door is quiet, and does not necessarily alert the next room of monsters that the players have arrived. Breaking down a door is a messy and loud affair. If any subterfuge is needed for players (be it in a noble's house or a dungeon) then breaking down the door is obviously not the best idea.

If there are no consequences for actions the players take, then they can do whatever they want with no fear of reprisal.

A possible solution to players breaking down doors willy-nilly is by making such objects have a damage threshold that means below the damage value the door cannot be hurt at all. This is a possibly confusing mechanic to spring on your players, so mentioning it beforehand would likely be a good idea.

We can look to real life to gain some insight:

Bank vaults in the US are rated to 4 different possibilities against forced entry:

• M 15 minutes


• Class I 30 minutes


• Class II 60 minutes


• Class III 120 minutes

Classified storage of national security secrets also have door certifications, the Class 5 vault doors being:

• 20 man-hours against surreptitious entry.


• 30 man-minutes against covert entry.


• 10 man-minutes against forced entry.

The door will only slow down a determined attacker, which is why there are also provisions for other required security:

3. For Top Secret information stored outside the United States, one or more of the following supplemental security controls is
   required:
   
   (a) The area that houses the security container or vault
   will be subject to the continuous protection of guard or duty
   personnel;
   
   (b) Guard or duty personnel will inspect the security
   container or vault at least once every 2 hours; or
   
   (c) The security
   container or vault will be controlled by an alarm system to which a
   force will respond in person within 15 minutes.

Bottom line: if modern national security vaults and banks can be breached in a matter of minutes via force, it's pretty likely dungeon doors and chests can as well. Add other security features if you want to truly secure something... and if they've killed all the guards, it's pretty reasonable to assume they can bang their way into almost anything if they want to take the time to do it.

The way our DM has protected chests in the past is having a manufacturer's notice in common that reads:

WARNING: Thank you for buying Thurlin's Secure Storage: this chest contains an anti-tamper acid ampule. Excessive movement or lifting of the lid without disengaging the lock will damage or destroy the contents of the chest.

and when we got used to breaking into those we ran into a:

WARNING: this chest contains explosive run... - boom

Everyone is talking about doors, but you also ask about chests. If you break open a chest, in Real Life, there's a fair chance that whatever's inside will get damaged, right? If there's something fragile inside, it might get smashed. If there's liquid inside, (inside a fragile bottle, for instance,) it might stain other items in the chest, for example making a precious scroll unreadable. You could introduce consequences to breaking the chest open instead of unlocking it.

Oops, I broke my axe

Weapons used to destroy a door or chest could be damaged in the process...

I don't think there's any rules about weapons taking damage normally (except some monsters causing corrosion), but it's reasonable that a nice sharp axe or sword could be damaged smashing up stuff made of wood & metal.

A "smashing" weapon like a hammer, or a crowbar specifically might have no problems, but anything else could be fair game.

Summary: A door is a tactical (sometimes, strategic) element with plenty of uses and a cost to manipulating it. Break it if you are in a hurry and enemies know of you, or if there are no enemies, while leave it functional if there is a chance of using it against your enemies.

Chests are similar but less complicated.

Breaking doors makes noise

Noise alerts creatures. The usual rate of wandering monster checks in large dungeons with mobile inhabitants is, for me, once every ten minutes, with 1/6 chance of encounter. I also roll after noise occurances, such as combat or breaking down doors. And, of course, any nearby creatures will often hear the noise automatically or with good chance. If breaking in takes significant time, that also triggers a wandering monster roll or moves the next one closer.

This is not an issue in places without wandering inhabitants, such as very small dungeons or ancient sealed tombs.

A broken door is a sign of forced entry

This is an issue in civilized or organized dungeons, such as cities and fortresses, or when trying to rob the ancient mage's tower without the ancient mage figuring it out.

Dead enemies everywhere is also a sign of forced entry, so this might not matter too much in many situations.

Doors control the movement of others, too

Wolves and unarmed zombies will have very hard time getting through sturdy wooden doors, even given time. Many enemies will spend at least a moment to penetrate a door, and might not be clever enough to open one. Doors can be barred for further security. In a typical dungeon environment with some animals or weaker creatures, doors can be used for good benefit.

Also, if one wants to rest within a dungeon, closing and barring a door creates a nice alarm system and might prevent some wandering monsters from reaching you at all.

Doors control vision (and sound a bit)

Controlling vision allows hiding and resting and makes ranged attacks a lot harder. Hiding behind a door to run away or surprise someone is a classic maneuver.

Not everything breaks doors

A rondel or a sword is not the proper tool for breaking a door - you would get a dull edge or a small hole, which is often not very useful. It would be a waste of a battle axe, too - use a woodcutter's axe or something similar. The rules of D&D 5 leave simulating such concerns on the dungeon master, whose duty it is to keep the game world credible. (We prefer to share this duty among the entire gaming group.)

The matter of chests

Chests protect things. Breaking a chest might break those things, or you might want to have a nice chest for other purposes, if it can be carried. The concerns of noise are there, as are leaving tracks.

The lock may actually defeat them

4-5 guys with a crowbar will eventually open any door/chest that's not magically locked.

Maybe.

I no longer have a reference to the article, but a few years ago there were a couple of thieves that figured out they could steal a freestanding ATM by tying a heavy chain around it and dragging it down the road behind their truck.

After a certain distance most of the pieces came off, however the steel reinforced part that contained the money was intact. At that point they lifted the remaining piece into the truck and drove off.

(The extra pieces and the scrape marks gouged in the road were easy to follow to that point.)

At some point after that, they gave up and tossed it into a creek where it was found by the authorities.

It was bent out of shape, but it still had all of the money inside it.

Maybe they were too dumb to steal a blowtorch, or maybe they were smart enough to realize that the blowtorch would burn the paper money inside... I don't know which.