In most thermodynamic cycles (either work producing or work consuming) there are 4 common processes as follows:
These 4 processes are always present. The fourth work input process is the one where compression or pumping of working fluid takes place. These processes require work input. Some part of work that is produced by turbine or engine is provided as work input. As this work goes back into the cycle it can not be used to do any external work. Hence it has to be subtracted from the work produced by turbine or engine.
This work output is less than the work produced at the turbine/engine.