"I've been largely operating via a classic RPG mentality of "clearing" every room even if the monsters are initially friendly." - Chester on the Camelot RPG.
Is that an RPG thing, a CRPG thing, or a TTRPG thing?
I'd say, "Classic CRPG mentality." You learn quickly in actual RPG to not kill everything just to kill it. Or you learn to accept the character casualty costs and opportunity costs of "clearing."
I'd say that from my perspective my players have exterminated a number of potential (and actual) friendlies, and closed off access to some really interesting information and actual treasures by "clearing" CRPG style instead of delving TTRPG style. I believe it's from coming from later gaming, where you have a feedback loop between later CRPG games and TTRPG games making "kill everything and search everywhere" the only way to play.
In a CRPG, you generally need to go to every square, explore every place, and kill every living (and unliving but animate) thing you encounter. You're not really "done" until you've done it all and especially killed it all.
In a TTRPG, especially an old-school megadungeon game, you really can't try to clear it all. It's a mistake to try. At some point you'll hit diminishing returns on the large but less valuable upper levels. That's in game terms. In real life terms, you can spend literal years in the same dungeon but never get very deep because you're trying to "complete" or "finish" or "clear" things. And you can all too easily get into the habit of trying to kill that which would rather negotiate or deal with you.
Sufficiently old CRPGs were generally like that. If you try the "clear it all" strategy in, say, Wizardry, you're making it hard on yourself. We won that game by eventually just taking a run at W*E*R*D*N*A by going down the elevators to level 9, skipping the intermediate levels, and casting TILTOWAIT while the fighters all attacked the evil wizard. "Clearing" the dungeon was impossible, so you learned not to do anything that cost more than it gave. You have to know what your goal is. And as I learned from Dan John, who I believe got this from Dan Gable (of "Gable grip" fame), you always have to keep the goal the goal.
In a really old-style TTRPG, that goal isn't clearing things. It's looting.