[atoav]

It is about how current draw is in or out of phase with voltage. Purely resistive loads won't affect the phase of the current. However if you have reactive loads like capacitors or inductors your current draw will either have its peak before the voltage has its peak, or after. This leaves you with less power.

In Germany going lower than cosphi 0.9 capacitive or cosphi 0.9 inductive requires special permission from the operator of the electrical grid.

If your installation affects the electrical grid in negative ways they can make you pay when something breaks or switch of your power to protect the grid.

On top of cosphi you also have ripple (basically "overtones" created by non-linear loads like unfiltered switching PSUs). If your THC (total harmonic current) exceeds 5% any power transformers in your net will have significantly reduced lifetime. But German grid operators allow a maximum THC of 15%.

So basically there are many ways how inductive, capacitive or switching loads can "deform" and shift the waveforms of the currents and voltages you are drawing, some of this can have negative effects on your own devices, some of it can have negative effects on the grid. Ideally you have a cosphi of 1 (so neither inductive nor capacitive) and a THC of 0% (no harmonics of the fundamental frequency present in the sine of the current drawn), but in reality you have to stay within what your grid operator allows.