I consider myself sort of a "Dynamic" DM. Meaning, when I write an adventure for my players, I have an outline and maps ready and then I "Go with the flow". I will have certain encounters prepared, like BBEG's etc, but the rest is free form and I try to judge how the flow of the game is going and how battered the characters are.
But even before I became that type of DM, I don't really remember wandering monsters stumbling on the party. I would always look at the table in the module, but I would inevitably skip right past it when we were actually playing the adventure. I'm not sure if I was too engrossed in what was in the next room or if I just forgot, but I never had random encounters. And to be honest, I don't think the players ever knew the difference.
Of course, there was always the ominous dice shake when the party was bedding down for the night, but I'm not even sure I ever had them encounter anything then either. I would just roll dice to keep them on their toes.
Do random encounters and wandering monsters add to the spontaneity of an adventure, or is it just a reason to cause a wee more damage? Am I missing half the fun by not having a group of orcs stumble on the party in the middle of the hallways rather than just having them sitting around a table gambling in the next room?
Now that I think about it, hallways always seemed to be sort of a "safe" zone for the party to plan their next action. A place to listen at doors and then decide how they were going to slaughter the rooms inhabitants. Heck, hallways are where you put traps, not random monsters. Maybe I have been missing something all these years. I need to rethink my whole DMing strategy.
Each door along the 10' wide hallway will be conspicuously labeled with the appropriate room number and what the mind flayer professor is teaching within. And believe me, this will be one dungeon where you don't wanna wind up in detention.