i quilt large quilts, queen +, as well as babies and wallhangings. so if i want to use it for a backing on a quilt unknown, then i buy 9 yds. that's backing + a little extra. if i know what it's for and i want to use it on the front as well, then i get more. otherwise, for stashing, if i really, really love it, must have it and can't live without it, then 4-5 yds. if i just love it, then 3 yds. if i like it very much, maybe 2-3 yards, like it 2 yds. don't like it, none. no fq's. never. but i only ever buy on clearance, not even on sale. either online or at a clearance center near me. and almost always on speculation. if i buy online i look for no shipping over a certain amount of dollars and find that amount or skip it. after a while, you learn what sites have the best prices and wait for their clearances. i never buy baby prints. applique using what i have always does the trick. same with holiday fabrics. i applique or embellish. it takes up a lot less space. if something is say, $2 a yard and i like it, i'll take it all. i also shop yard sales. when i cut into fabric i try to remember to measure and mark the rest of it. i don't mark the cost. it doesn't matter anymore. i don't sell my quilts, and that info would be outdated anyway.
i have a very big stash from years of quilting and sewing. i keep it by color in huge plastic tubs that are overstuffed and i can't see into them. that has to change soon. they were left over from something else. i also have fabric on open shelves and that must change soon. too dusty. i'm thinking of buying glass ikea doors and having dh hang shelves to fit the doors. the ikea cupboards themselves are mostly too shallow.
phew! that's a mouthful!