I didn't do this on a block I had used for my daughter's quilt I made for her wedding. It was a stash buster block in one of the magazines and I just kind of figured it would work. Needless to say, it cost a whole lot more than it should have. I now make blocks to make sure they work, and I put them in a sheet protector and binder with my patterns, or I make them into hot pads.
My reason for realizing I had to do a sample block from now on, was because there was a misprint in the instructions. It has saved me some good money to do this extra step.