I would have to agree with the majority of people who have answered. 98% of the quilts I make are scrappy and I draw upon my fabric collection that spans 40 years. It doesn't bother me a bit to put a batik next to a Civil War reproduction if the colors and values work for that particular quilt.
I do think that the collections of fabric can be very helpful for newer quilters who haven't amassed a stash yet or who are less confident about their color-choosing abilities. And for those who don't prewash, precuts do save time -- there is something to be said for being able to come home with your goodies and immediately start sewing! I know a couple quilters with small children who honestly don't have the time to do much prep work before they sit down to sew ...