I understand that if supply and demand are not in equilibrium synchronous generators make the difference by increasing or decreasing their rotational energy - thus changing the electrical frequency in the grid. It is usually noted that a frequency shift $\geq 1\%$ is unacceptable and might damage the grid; however, I cannot find anywhere what in particular such frequency shift can damage. Which components of the grid are the ones we are mostly scared of getting damaged?
I am also curious what are the usual methods of mitigation of such situations, if I understand correctly, if the generated power is much higher than the demand the power stations disconnect and a blackout occurs (i.e. on a very windy night in a country powered by wind power stations). Similarly when the demand is much higher than the supply then some areal blackouts are purposefully introduced to decrease the load.
Lastly, are there currently any methods - beyond classical generators - that are widely used to increase the grid inertia?