In effect, you don't really have to but they are pretty cool. For example, when I got the first anti-grav power, I found it really useful to launch enemies into the air and while floating, picking them off with weapons. It was helpful while I was still low level to take out higher level enemies. Also useful for pushing them of something from a great height
I guess you could ignore them and shoot your way through the game but if you add them to a slot in your favourite hotkeys along with your weapons, they are a pretty solid extra addition to make life easier.