Recently I came across a question where they have asked which of the options is a unit of power. It had both kVA and kW in options. My teacher told me that the former is used as per rating ( neglecting the power factor) and latter is used for actual power. 

This had me confused. Aren't they both the same? Is this similar to the case where we say joules is unit of energy but not torque. So when two units have same dimensions, do we have to follow a convention to use them? 

Wikipedia says kWH is a derived UNIT of energy. Now, is it based solely on the fact that they have same dimensions or is it because it is commonly used and thus, accepted. Would it be alright if I refer to unit of force as $\operatorname{kg} \operatorname{m}/\operatorname{s}^2$?