If I want to quilt as soon as the quilt is basted, I press after gluing. It evens out the glue spots if any. Evaporates all the water out of the glue so no wrinkles when drying. If a pucker or wrinkle use steam to loosen the glue to re position that spot. One time I changed my mine about the backing after it had been glued basted for weeks. I ironed glued basted another backing on top of the backing I didn't like. Worked great.