Well, I do know that some combustion turbine (my preferred term over "gas turbine") plants feed the turbine exhaust into a boiler (aka "heat recovery steam generator") and then the steam can either go to a steam turbine (combined cycle) for more electricity or be used for heating or as process steam (co-generation).
Previously turbine power plants were used mostly for peaking plants not for base load but combined cycle ups the efficiency enough to make them useful for base load despite using premium fuels (lighter oil or natural gas).