As a quilter, I like pre-washed fabrics better to quilt on. The needle passes through the fabric more smoothly. I like sewing with pre-washed fabrics also. I don't like the stiffness some new fabrics have. I've also found, if I pre-wash my fabric right away, I can get a better idea of how the fabric will be in a finished product. And I LOVE taking my new fabrics out of the dryer after they've been washed. I think they look better and feel better and then I know they're all ready to go.
I guess it's whatever you're used to and personal preference. Oh, and I never wash my quilts before giving them...maybe because they fabrics already been washed? I've started giving my clients a little sample sandwich that's been washed and dried with instructions so they know what their quilt will look like when it's been washed.
I've been doing a lot of Quilts of Valor quilting and am surprised at how few people pre-wash their fabrics...all those red, white and blues...I'd hate for them to fade or run in the wash cycle, but once it's pieced, there's not much that can be done.