I do have a longarm so my results may be different. But I usually do press the wrinkles out....but my criteria for if it is pressed good enough is if I can still feel the wrinkle when I pass my hand over it. Sometimes, I can still "see" the wrinkle but it feels smooth. I have found if I do this, by the time I load the backing on the quilt and quilt it, those wrinkles that I can "see" but not "feel" are gone. I know a professional long arm who does not press backings brought to her by a customer unless the wrinkles are really definite and the fabric just will not lay flat at all, she says that by the time the fabric is rolled on the rails and the quilting is done, the fabric usually relaxes.