I almost always buy yardage, but I'm careful about it. There are certain places I go where I know I'm going to find great fabric at clearance prices. The bargain bin at Keepsake Quilting is one, and the clearance fabrics at Connecting Threads is another. I have a couple of other "proven" on line sources, and a couple of local sources. I made out Big when Keepsake Quilting did that week-long 40% off all fabrics in their bargin bin, and I try not to buy fabrics from Connecting Threads that are more than $3.50 -$4.00/yard. I've found terrific fabric there for under $2.50/yard. I try not to pay more than $5.00/yard. I have my lists my things I need: blue focus fabric, tan background fabric, coral background fabric, etc., etc. And as I cruise through my sites monthly, I'm looking for fabrics I need, although if I find something I can't live without, well, that ends up in my basket too. I'll buy anywhere from 3-5 yards, depending on whether it's a focus fabric, or a background I can use in lots of places. I've been know to buy more than that for something I dearly love (up to 9 yards) and expect to make use of in a big way. There is nothing like planning a quilt, going to my stash, and pulling out every fabric I need without any additional trips to the fabric store, unless it's for thread. Anything left over can be made into Fat Quarters or Jelly Rolls, which are nice to have on hand -- in colors and patterns
I like! Or I leave it as fabric if there's enough left. So that's my strategy!