both!
body loves repetition and pattern so it can adapt and stagnate, the lazy bastard.
gotta throw it off, sets of perfect form using max weight for that form, TUT etc.
Mixed with sets or days of lesser form and heavier weight, more explosiveness to overload muscle and add new stress.
Still need to hit target muscle effectively though, but things like turnaround point of rep and force generated are really emphasized with heavier poundage so sacrificing a bit of form to achieve this isn't bad at all.
Poundstone had a good saying, everything can work but nothing can work forever. Need to add new stimulus and stress.