The hands are for punching! Obviously.
I wonder how useful the hands on any 'Mech are. I mean, on the smaller scout mechs, it kinda makes sense, if you're actually using them as scouts. They'd have to bend trees back while bushwhacking, or might need to rip open a hangar door if they're on an espionage mission. But otherwise, it's my understanding that the control systems are too clunky for hands to be much use on any mech, except for modular weaponry. But the only ones that I remember which actually carried handheld rifles are the incubus, Wasp and Valkyrie, all of which had to be removed due to copyright stuff if I'm not mistaken.
And later designs for the valkyrie and wasp featured integrated weapons, which makes the incubus the only one I know of that uses handheld.