If I'm piecing, I just start at one end of the piece and end at the other, no backstitching required since I will be sewing over those starting and ending points with other seams that will anchor them. When machine quilting, I do backstitch the start and ends since those will not be stitched over (they will be stitched by). So the rule of thumb is that if you are going to eventually stitch over the start or end of the thread, I don't think there's a need to anchor the start or end with a backstitch.
Ooops, I just reread your post, you are talking about quilting, not piecing. So I always backstitch to start and stop quilting.