for me i dont have cns in mind but i wanna be comfortable with a weight performance wise... let's say i barely get 8 reps, then im not in the position to go 9 reps a few days later... i rather make it clear that i "own" that 8 rep and can do it with good form... but it depends on exercise, some are easier than others to add weight to
some do add microweights etc and it does make sense let's say you focus on your bench and eventually adding small weights to the bar will add up over time, but to actually do it is another story, i cant say i personally bother with it...
then there's other ways to work with the intensity etc like shortening rest between sets and so on
but it might be different depending on your goals. like i said, if getting a better bench was my #1 priority i might be more scientific about it