When I find a great price on prequilted fabric, I always buy about three to four yards if it is a color combo that I like, as long as it is double sided. I do not buy one sided prequilted. I use my finds for gift bags, purse linings, baby blankets, baby snow suits, etc. if I were going to practice on a long arm, I would chose two versatile fabrics that I could do the same with. That way even though I might not love the whole thing, I could cut the parts I like into smaller projects, or use a solid on the back and some kind of print that I can follow with the quilting to practice control and following lines. I just can't think of a piece of fabric as "waste".