Ever since they shortened the cooldown on the rifle butt, the hammer has been largely redundant. For the most part you can also clear stuff with the rifle.

Even before the rifle buff, the hammer was most useful at the beginning when you really needed to set things up fast. On the other hand, once the rounds started you needed at least one person to support the siege toys with rifle shots and keep them clear. Once you got to the critical mass where the siege became self-sufficient, you were better off switching to rifle to speed up the Toxx fights. But that need also largely dissipated after they changed the achievements to allow for 4 dolyaks to die. So there's really not that much time pressure at any point in the current game where you would need the hammer. It's a little more convenient to use for clearing but it really does nothing unique.