There is no difference between power factor and displacement factor. The power factor is the cosine of the angle between the current and the voltage, which is also known as displacement power factor.

power factor means kw/kva

Output Power divided by Power Factor.

There is no disadvantage of unity power factor, because at unity power factor all the electrical power is efficiently utilized by the the load, and at lagging power factor some power is lost in the load's magneticfield.

When looking at power factor, it is the ratio of watts (true power) to VA. The power factor is how we measure power systems. A person with a low power factor like .26 will have a higher electricity bill.