I think people underestimate the value of intertia in power generation. I liken it to the way capacitors regulate voltage changes or coilovers absorb bumps and vibrations.

The inertia of the generators connected to the grid helps stabilize frequency changes caused by blackouts, power plant issues, etc. by resisting and thereby slowing down frequency decline. It buys time for grid operators to find a way to balance loads in a way that doesn’t weaken or disable the grid as a whole.

Here’s a great NREL report explaining how this all works, and what other systems we use to stabilize grid frequency.