Real, reactive, and apparent power aren't three ways of measuring the same thing — they're three genuinely different quantities, and only one of them is what your wires and breakers actually have to survive.
Say "power" to most people and they picture a single number — how much a load draws. In AC systems with motors, transformers, or anything with a coil in it, that single number splits into three related but distinct quantities: the power that does useful work, the power that sloshes back and forth doing no net work at all, and the power that determines how big your equipment actually has to be. Confusing any two of them is how you end up under-sizing a transformer or getting hit with a utility penalty you don't understand.