I have one customer who always wants 1" of backing and batting left when she wants me to trim after quilting, she actually attaches her binding to the top then trims ....seems to work for her. Some prefer I do not trim at all... Some want the whole thing squared up, so may involve cutting some of the top too...its a personal choice and a quilter should never Assume, the customer should be asked what their preference is. For my personal quilts it really depends on the quilt, the planned binding, my plans-- so, I do not Always do it one way... I do it the way that quilt needs to be done.