I've never heard of this either. I have pressed tops and backings at the quilters request but I charge for it ( unless its a quick touch up) but never after quilting. Sometimes people don't like to press and prefer to pay to have it done or they have physical problems that make it difficult.

I have never pressed a customer's quilt after it was quilted. Sometimes before if they were shipped to me and some wrinkles.

i have a longarm an no i have never pressed seam after quilting i think seams will set when they are washed