I've blogged before about magically barring and opening doors as well as secret doors, but a recent thread on Dragonsfoot got me looking over the text on just plain old doors in dungeons.
Moldvay (B21) says:
NORMAL DOORS: Doors in a dungeon are usually closed, and are often stuck or locked. A lock must usually be picked by a thief. An unlocked door must be forced open to pass through it. To force open a door, roll Id6; a result of 1 or 2 (on Id6) means that the door is forced open. The roll should be adjusted by a character's Strength score adjustment. The number needed to open a door can never be less than 1 nor greater than 1-5.
Once a door is opened, it will usually swing shut when released unless it is spiked or wedged open. Doors will usually open automatically for monsters, unless the door is held, spiked, or closed with magical spells.There's a lot to unpack here, given such a short entry, but that's part of BX's beauty, IMO.
First off, nearly everything described about doors is qualified with terms like "usually" or "often," leaving room for the DM to use their discretion and judgement. The language helps paint a picture of what dungeons are usually like. Doors warped and swollen in their frames bu the damp, or latches rusted shut. If it's a more heavily used location, like an active lair, perhaps a stuck door is rarer. Locks are still a thing, though.
This brings us to the next part: opening said doors. Locks are a thief's job, obviously. Of course a failed roll could lead to a brawny PC forcing it open as if it were stuck. This gives a sense of how these obstacles are expected to be handled. The smart party tries stealth first, force second.
The last part of this section seems at first a bit "gamey" in its language. Doors just swinging shut and especially the part about them simply opening automatically for the monsters. My own interpretation of this is that the location's denizens know the place well and are used to the doors' fiddly little ways. I wouldn't have a door just pop open for a creature that couldn't normally operate it, e.g. no hands or unintelligent.
As far as swinging shut, I interpret that as doors that no longer hang true on their hinges and naturally fall back closed. Again, this isn't every door all the time, but it can happen.
So all this begs the question of why? Why have door stick and slam shut? Why make it so the party has to take the time and effort to pick its lock, or force it open? The answer is time. All these efforts cost the party time. As classic D&D is a game of resource management and exploration, the players will have to make choices. Do we waste another turn trying to pick this lock? Do we risk attracting some wandering monster's attention with the noise of forcing open this door? How long until the current torch burns out?
But what if that's the door that leads to the PCs' goal? Or the lower levels? Aren't you just screwing with them by leaving whether the game progresses up to chance like that?
While you certainly can run a "pure" sandbox like that, with zero plot or plan; most experienced DMs follow the guideline of either A) not putting something critical out of reach because of one bad die roll, or B) Always have more than one way for the party to move forward. Maybe the lock is too tough for the thief and the door is too strong to be battered down. However, maybe there's a secret door they could find that will let them through? Or maybe there's a key to be found? I'm not suggesting this be the case with every door, and I admit it's still possible for bad luck to derail things, but used judiciously these wrinkles can add a lot of detail to an adventure.