Great explanation by Olympic A-340.
The reason why to practice a lot of power-on stalls is, as said above, to be able to recognize the handling characteristics of the airplane and the recovery with minimum altitude loss on such situation. The power-on emulates an over-rotation or excessive angle of attack during take off. Remember that you are defying the laws of gravity, that your airplane is flying slow, really close to the ground and with such great power that the nasty left-turning tendencies are at their most. A properly developed recovery technique will make the airplane maintain directional control, reduce the excessive angle of attack and gain airspeed (and thus lift).
On the other hand, the power-off will get you familiar with the characteristics of a stall while on landing configuration. The outcome of a well performed maneuver will maintain direction, reduce de AOA and gain numbers in the AI
Two out of many things which do you no good in aviation:
- Altitude above you.
- The airspeed you don't have.
Keep the blue side up !
There are no stupid questions... just stupid people!