My preference is to do two blocks at a time, building my quilt top. When doing Bonnie Hunter's mystery I will do as instructed, but I personally like to build and make sure things are coming together well rather than assembling all parts at the end. even with making a test block, I usually have some regrets - wishing I hadn't pressed all hst to the dark or something like that... Another reason I prefer to make blocks a couple at a time is that as they accumulate on the design wall I can tweak colors.