i think there are things to consider:
1. where did you get the fabric...chain stores rather than first quality quilt shop fabrics can react differently, so those i would pre-wash.
2. scrap quilt with mixed manufacturers i would pre-wash
3. dark colors going into applique quilts with light backgrounds I would pre-wash
4. flannel quilts for a baby that are likely to get washed many times, i may pre-wash (not agitate, just wet them, spin them and dry them).
when i make quilts as samples for new patterns or fabric collections, there is no time to pre-wash. The quilts are washed when finished. I like the vintage look that i get when quilts are washed after...I use dream cotton batting or hobbs 80/20, and do a lot of quilting. There is probaly not a rule that fits all quilts all the time for me.
Quilts should not be washed in hot water, or dried in a hot dryer. cool water, low-moderate heat dryer setting, 10 minutes at a time. Not until they are bone dry...just dry enough not to bleed if fabrics are suspicious, then laid flat to finish drying.
If a fabric is going to shrink, you can see it happen under your iron if you are using spray starch to mist the fabric before the iron hits it.
Scrap fabrics with mixed manufacturers and mixed purchase sources i would pre-wash for sure.
And if the backing fabric is not the same manufacturer as the top fabric, i would recommend washing that also. I know lot of folks try to save money by using a less expensive backing, and if that shrinks after the quilt is done, it can truly ruin the whole quilt (don't ask me how i know)