Generating electricity creates mechanical load on the generators that in turns allows to discharge the energy in generated high pressure steam.
At some point you hit a case where you can't go lower without shutting down completely, and that involves all parts of the system - just spinning up or down a steam turbine can be a harrowing moment as depending on the whole setup there could be an RPM range where the harmonic oscillation might destroy the whole thing (as my grandfather, who was working as engineer on steam turbines for electricity generation, described it: "we would slowly spin the turbine to the critical RPM range, then open the throttle to cross the critical range in as short time as possible, then do slow and steady to the rated RPM")
At some point you hit a case where you can't go lower without shutting down completely, and that involves all parts of the system - just spinning up or down a steam turbine can be a harrowing moment as depending on the whole setup there could be an RPM range where the harmonic oscillation might destroy the whole thing (as my grandfather, who was working as engineer on steam turbines for electricity generation, described it: "we would slowly spin the turbine to the critical RPM range, then open the throttle to cross the critical range in as short time as possible, then do slow and steady to the rated RPM")