Hello brother
Look at your question, I relate it to cash desks.
In an MTT with players you know, you see situations, study their game, etc. situations that can be beneficial to you.
An example would be that if you do 3bet AK from any position, the opponent knows how you play and will think before raising, equalizing or retiring.
Instead of playing with amateurs or at a cash table playing only against someone who has money, there are no schemes or manuals.
You have AK and the opponent thought of 23 that would beat you and can match your bet, so match... the flop is 227 and the story ends.
That's why I think that if you have a good knowledge of poker and you play at an amateur or cash table, at least I don't underestimate any player. Rather, I would act at least at first very cautiously.
Cheers