Just to give them a little taste of the action with no pressure.
The Leafs are in a dog fight for a playoff spot. Now is not the time to call up bodies just for the sake of giving them a 'taste' of the action with no pressure. So long as the Leafs remain in the playoff race, there is absolutely pressure - from the top of the line up all the way to the bottom.
Hamilton is an awesome character player to have in the lineup, especially once the playoffs come around. My only knock on the guy is that he's not the greatest skater, but that shouldn't be a problem if his minutes are minimal/not against top players.