I buy more according to how the piece looks. I sometimes look long and hard to find a suitable piece. If it has the grain and color I'm looking for, and meets the minimum size I need, I buy it. If I can get 2, 3, or 6 bows out of it, great. I've bought some rather large pieces of exotic wood riser material. When it's bigger than I need, I can conveniently get matching overlays off of it.