Electrical power is measured in watts (W): The voltage times the current measured each instant. In a direct current system or for resistive loads, the wattage and VA measurements will be identical. But for reactive loads, the voltage and current are out of phase and the volt-ampere spec will be greater than the wattage.
For determining power, watts are appropriate. For determining capacity for the driving circuits (circuit breakers, wiring, and uninterruptible power supplies, for instance), VA is appropriate.