Propulsion (Control, D-Pad Left)
Re-routing your power to propulsion will help you go a lot faster when in flight, faster than normal, but only make use of this when you need to speed up towards a distant object.
Armor (D-Pad Up)
This will truly make you Iron Man as re-routing your power to armor will lower your risks of damage more than usual while, at the same time, increasing your very own melee damage as well.
Weapons (Control, D-Pad Right)
Re-routing your power to weapons will replace your repulsor with the Unibeam which, upon being fully charged, unleashes an extremely powerful shot.
Even (Control, D-Pad Down)
Re-routing all of your power evenly will reset all your systems to balanced power distribution. Highly recommended unless one of the above is necessary (afterwards, reset back to even).