Doors get an awful lot of attention in D&D. They do present a barrier at the threshold to what lies beyond of course but the handling of doors in the original game is a bit...boring and really shapes the game in an odd way. All doors stick shut requiring a roll to force open if not pegged so as to stay open and all monsters can pass such "stuck" doors without challenge.
I'm not going to promote equal treatment of pcs and monsters here, what am doing is pointing out the ever present stuck door is boring and a play barrier. Such stuck doors should be a feature of a dungeon or dungeon level not everywhere.
Unstick those doors let PCs walk on thru when not barred or locked. It increases mobility and makes it easier to trick players with door traps once they get a little careless.