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 best way to think about it is a literal flywheel, because that's what this is, just at a grid scale, and directly tied to the frequency.

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.

TLDR it moves the "OH SHIT OH FUCK" window from about < 1ms worth of time in the worst cases, to the much more manageable, seconds window.

It's a potential challenge with moving to renewables, but not a significant one, i think. This is also a big advantage to having sources based on thermal generation, like nuclear.