Yes, because their is less power lost going through the esc. Contrary to popular belief, electrons flow from positive to negative. Now, how much of a boost is arguable.

Power capacitors act like miniature batteries. When you punch the throttle, there is a slight drop in power normally with the huge sudden amperage draw. A capacitor helps to keep the power going to the motor consistent under the loads. It "recharges" itself when the car is running. All the brushless escs on the market have one installed.