Hello,
from What I remember in college,
The nature of our appliances at home is somewhat purely inductive, so the imaginary component is producing a big phase angle difference between the real power and the reactive power.
What the device do is (Simple capacitor with bleeder) will introduce a capacitive load and will try to cancel the big phase angle.
If you will imagine a triangle, real power is the base, while reactive power is the leg. the hypotenous (Sorry if I got it mis-spelled) is the power that we pay for in our bill. so the smaller the phase angle the lesser our bill.