This is necessary in any application where rotary motion is used in preference to the energy contained in the thrust of the turbine.
Examples of this include: combined heat and power installations, generators, turbo-prop engines, helicopters and ships.

The hot wheel is an extra set of turbine blades which are acted upon by the hot gas produced in the engine. The induced rotation of this hot wheel is transferred to a usable location outside the engine casing via a coaxial power take off shaft and a gear box.