Is the jet used to superheat water, or directly drive a turbine generator? If the latter, it would be a waste of time, if the former then you just want heat, a

Is the jet used to superheat water, or directly drive a turbine generator? If the latter, it would be a waste of time, if the former then you just want heat, and the fan is there to provide enough oxygen to burn the fuel so why would it impact efficiency? Edit: I was thinking literal jet engines that have indeed been used as generators, not combined cycle generators.