My experience is that in the few places that rip the fabric, I have less waste. I don't know how many times I have had to cut off quite a bit of fabric to get it square. It makes me mad when I end up with less than the yard I purchased, and I would rather deal with the threads. I have a friend that got to the bottom of the quilt she was quilting to discover she was short fabric on one side. She trimmed the top but didn't worry about the bottom. If I remember correctly, she had purchase a 1/4 yard of extra fabric than needed for machine quilting on a frame. Personnally I always buy about about 1/2 yard extra and now this friend does as well.
Some I rip at home (I was raised to rip fabric when squaring it up). My sis almost always rips backing fabric.