Do what works for you. I was into thrift shopping quite a bit a few years ago and I bought a lot of stash at cheap prices. Since we didn't have a lot of $ coming in, it was the only way I felt comfortable taking up quilting as a hobby. Besides, if I bought a lot of expensive fabrics and then didn't like it, I'd have been really unhappy.
Now that I've about reached my space limitations I have stopped buying unless it's for a specific project and I have nothing in my stash, like most of my stash is washed and I wanted to do a OBW which requires an unwashed piece...so I bought for that.
Most all of the 8 or 9 completed quilts and the 4 or 5 tops I've made so far have been mostly or completely made from fabric on hand. I got into log cabins using 2 1/2 inch strips and just cut, pieced and quilted up a storm for quite a while. Now, I'm trying to move on to different patterns, still using mostly fabric on hand.