If you decide to wash the quilt top that's already together, pin it into an 18" square with safety pins and put it in a mesh bag (like for lingerie), then wash it on gentle cycle. Use a color catcher, of course. When you take it out of the washer, remove all the pins and dry it in the dryer. The dryer doesn't cause raveling like the washer does, so taking the pins out will be ok.
I did this for my nephews quilt and it worked fine. Was it necessary? Probably not.