I am another who buys both precuts and yardage.
I have bought Daily Deals from Missouri Star, FQ bundles from MassDrop and Craftsy.
I wash yardage and do not wash precuts and have used them in the same quilt or project without issue.
I like the variety in precuts, I have made several quilts with Jelly Rolls from the Jelly Roll Race to one that looks like a big gift with a bow. I do not have photos of them.
I have used a jelly roll and charm pack to make a square in square quilt, plus yardage from the line for the borders.
I like the quick and easy patterns Missouri Star features each week using precuts.
I am fairly accurate in my cutting and have an Acquilt Go cutter.
The only tip I can share and it took me awhile to learn this, is if you think you will need yardage to complete a quilt (borders, binding, sashing etc), buy it when you buy the precut, otherwise you may be out of luck.