In a heat engine such as the gas turbine the fuel is "paid for" and the turbine shaft work is "what you get" (together with the thrust produced by the gases leaving the nozzle in an aircraft application). 

In terms of the specific enthalpy at each point in the cycle for a stationary power plant where turbine shaft work is desired as an output, the net work output is the difference between the turbine work per unit mass flow and the component of this work used to drive the compressor 
                                 W_out = (W_turbine- W_compressor).
Writing this in terms of the specific enthalpy drop across the turbine (h₃ - h₄) and the specific enthalpy increase across the compressor (h₂ - h₁), and dividing by the specific enthalpy input due to combustion 
(h₃ - h₂) gives the shaft work efficiency of the cycle: 
                          h = {(h₃ - h₄) - (h₂ - h₁)}/(h₃ - h₂).