I usually have a pretty good idea of what I'll use the fabric for when I buy it, borders, focus, highlights, blenders, etc and I also know what sizes of quilts I generally make. Anything that's a highlight or blender where I'm likely to use more than one fabric of the same color I get a yard or two. For a focus or border fabric I never buy less than 3 yards. If I think there's a good chance I'll use it for both the borders and the focus I'll get 7 yards. If it's something that's on a sale rack and less than $5 a yard I'm very likely to just buy what's left. I've run across several sales where the fabric was $2 a yard or $1 a yard if you bought it all.