New players
I have something interesting to add. I lately started to introduce a group of newbies to the game. They had never played D&D except two of the 7 guys and gals.
I used no designed encounters. Only Status Quo stuff with evolving NPCs. It was not a problem. The players didn't know anything about how tough monsters can be, that trolls fear fire or whatever. If I told them about that 8ft high thing with a club longer than the dwarf, they ran or tried to shoot it.
In another group I got the players use to kill themselves even in designed encounters. Sometimes they whine later why I made the monsters too tough. (Grrrr, they killed the tough encounters easily)
So IME, the whole problem with Status Quo encounters is metagaming. Take players who don't have all MM statistics in their heads and they will be cautious.