It is a thought process you have to practice. I am a firm believer that stabilizer is the foundation of a good design. Fabric assumes the qualities of backing, therefore fabric can be made more stable by using the correct backing. Sheriff's rule of thumb is, if fabric stretches, use cutaway, if it doesn't, use tearaway. I always use cutaway on denim.
Many embroiderers think tearaway backing is OK for knits.
It may look fine when it comes out of the hoop, but after a few washings, the tearaway is going to come out. Once tearaway is punctured it loses stability. Kim Fillmore, education manager for Pfaff in Paramus, N.J., agrees the best design in the world won't come out nice if the fabric is not properly stabilized. I prefer cutaway stabilizer on knits because it doesn't perforate around the edge. Heavy embroidery on tearaways will perforate the paper and your garment is no longer stabilized.