Actually, the job of the rocket is to to increase the potential energy of the payload, so using a He balloon to put some distance between the rocket/payload package and the ground is an entirely sensible proposition.
Most of what the rocket has to increase to take an object from the earth's surface to LEO. If you calculate the potential energy of a rocket in LEO and compare it to its kinetic energy, you'll find the latter is much larger. (I've already done this and posted it here.)
