Yes as above it's to indicate which button to press to reset power distribution to 2 pips each. In fact you are controlling the recharge amount to the power distribution module, which then supplies the power to the 3 main areas. An A rated module has a higher capacity than a B rated of the same class and so on.
Increasing the power to weapons does not give you more powerful lasers for example, it just increases the recharge rate to the distributor. In other words if you have no pips or 4 pips to weapons, (and there is sufficient charge) the lasers will do the same damage. At the moment you cannot "overload" a weapon like you can with phasers in Star Trek (!) In the PC version the default keys are down arrow (not on the keypad) for Reset, System is left arrow to increase. Engines is up arrow to increase and Weapons is right arrow to increase.