The power equations for a circuits have two different means.  The First equations P = IV is the rate of energy released by the power source, or simply put the power "produced" by power sources.  Remember that energy isn't created instead it's transformed, the power source "transformed" types of chemical or mechanical energy into electric energy.  

  The second equation is the power consumption equation.  Remember that resistors "consumes" potential.  As the voltage is lowered in each resistor so each resistor is "consuming" energy at a rate, or simply put the power "consumed".  But energy can't be lost just transformed, in most cases the energy is transformed into thermal energy, but in cases like light bulbs the energy is also transformed into light.

Important Equations

P = Power 

I = Current 

V = Voltage 

R = Resistance

Power in a Circuit