Yes. Sometimes it takes awhile for me to get the technique down, so I don't cut into my "good" fabric until I can do it reasonably well. Also, sometimes what looks good is a big pain to make up, and I don't want to find out AFTER cutting all my good fabric up.
I have started doing all my test blocks in a one set of colors so that eventually I'll have a sampler top for charity.
Also sometimes I re-size blocks and it takes a little fiddling to get everything the right size.