You could know, going forward what you'll likely use, by looking backward.
Your last 10 or 15 quilts used what size strips or squares? Cut accordingly.
For me, I'm never going to use a 3.5 square in my quilts, totally enormous.
I have in the past cut 1.5" squares happily, from the smallest bits but I have a suitcase full of 2" four patches now, so am consigning those bits now to the trashbin of well earned retirement.
I do cut 1.5" strips though and use them a lot in colors I need at the moment.
So 2" and 2.5" are what I cut to, strips or squares.