What is the use of reactive power in electric circuitry?

'Reactive Power', which is expressed in reactive volt amperes, describes the rate at which energy is alternately stored (in a circuit's electric or magnetic field) and returned to the a.c. supply when the field collapses. It differs from true power, expressed in watts, because true power describes the rate at which energy is permanently lost by heat transfer due to the resistive component of the circuit.

Reactive power doesn't 'have an use', per se, it's merely a way of quantifying the movement of energy in the reactive component of an a.c. circuit.

The vector sum of a circuit's reactive power and its true power is called the apparent power of the circuit, expressed in volt amperes.