I worked for a quilt/decorator fabric shop when I started quilting (it's where I got bit by the bug, actually). I bought yardage when I had a specific project, and bought out of our 1/4 yd scrap bins when something caught my eye. Now I have a ton of 1/4 yd pieces that I don't know what to do with!!
I'd either buy for patterns or buy in minimum of 1 yd cuts, if you're looking to build a useable stash.