What are static capacitors?

These are capacitors that are connected in a circuit in parallel with the load. A circuit with low, lagging (inductive) power factor (pf) can be improved by those static capacitors by decreasing the circuit's inductive reactive power (wasted power consumed for magnetic induction of motors) reducing it's pf to almost unity (1).

A circuit with low power factor means it consumes more power which is actually not being used or wasted. Putting a static capacitor for pf correction improves the circuit.

Power-factor improvement doesn't 'improve the circuit', and it has no effect on the power of a load, it merely reduces its load current.