What is mean by mechanical efficiency of gas turbine and significance?

the mechanical efficiency of GT is is the relationship between the total energy contained in the fuel, and the amount of energy used to perform useful work. where 60% of GT energy will consume to rotate the compressor & the remaining energy will convert to electrical energy. usually the efficiency of the GT around 27% to 36 % depend on the size of the GT , type of fuel & site condition.

usually in operation we can accept to run the GT if the loss in the efficiency less than 3 MW until we have chance to shutdwon the units & invistegate the efficiency drop ( some time need water wash or has air leakage etc..)