For me it depends. I found a piece with hummingbirds on it, and I bought 1 yard, not knowing how I would make it, but my mil loves hummingbirds. I found the perfect pattern, it is dusty meadows, in one of the 2008 issues of quiltmaker magazine. I did do some fussy cutting, but I think it will be gorgeous when I get it done.
Sometimes, I will see a pattern that I like, and will just wait till I find the perfect fabric. Sometimes if I know who the quilt is for, it helps me know what colors I want to go with.