It depends. I just finished a queen size for my grandson. It's made entirely of batiks. I'll be washing it before I give it to him because when I prewashed all the batiks, a couple pf them ran. I was careful to rinse and rinse again with vinegar until they no longer ran, but I want to wash the whole quilt with a "Color Catcher" sheet just in case. If the sheet turns very dark, I'll know the quilt needs to be rinsed again. Although I doubt it will, one can't be too careful.
Other than that, I usually don't wash because like others on this thread, I like the new, crisp look. 8-)