I press as i go, and before sending it off to the quilter I make sure everything is perfect; she loves to quilt it when it lays flat when she puts the trio together for quilting.
Since I'm a new quilter, she is amazed I bring it to her in such fine shape. She says many of the old quilters just bring her a couple tops that are rolled up, wrinkled and she refuses to do their cleanup work for them, so there is threads at times, and of course if she sees them, she does remove them, but she makes no big attempt to remove what they could remove. Also, it lays so much nicer when she wants to go to quilting it - and I've been so pleased with the outcome of the quilt(s) when done.