Generalized Power Equation, Ohm's Law and Ohm's Power Loss?
At any instant, if a circuit is drawing current I from a voltage source of emf V, then this means the voltage source is delivering P = VI joules per second to the circuit at that instant. 

How the circuit uses that energy is upto the circuit:
 - If the circuit has an incandascent bulb, the energy is used to produce light + heat.
 - If the circuit has a motor, the energy is used to do
   mechanical work + heat.
 - If the circuit has a speaker, the energy is used to vibrate the diaphragm of the speaker + heat.

Note that power can be positive, negative or 0:
If VI is positive, then the voltage source is actually giving power to the circuit. However, if VI is negative then the circuit is giving power to the voltage source(battery charging circuit).