Anytime I dig and divide daylilies, I always cut off the tops to within about 6 inches from the crown. Not sure if it helps with the roots, but it keeps the tops from flopping all over the place.
Some people think that daylilies are like daffodils and crocuses that have bulbs, which the foliage does help to feed the bulbs. But I don't think that is the case with daylilies.
