I always do a practice sandwich with each project. That being said, the practice sandwich is the same fabrics and batting and thread which I plan to use on my project. I do this to not only warm up my FMQ technique, but also to test the tensions, look of thread with fabric and get the feel of that fabric under my machine and hands.
I agree, a sample does not handle the same as a project, but I feel it is a great habit for checking last minute settings and adjustments.