His theory is that there isn't enough puck to go around for three skill guys on a line. He believes every unit needs a "puck retriever" ie hard worker to do all the little things in order to free up the skill guys to do their thing.
Hyman in particular is a guy Babcock has claimed to be one of the league's best forecheckers and retrievers, which is why he sees him as a fit to play with his skill guys.