Following a fault, when the voltage on the line is trying to come back, there can be a case where if the line is not "strong" enough (higher impedence), then all motors coming back on line together present such a reactive load that it can make it impossible for the voltage to come back up, leaving the line at 50% or less of nominal for some time (or indefinately, until something trips) doing all kinds of damage. I guess this is especially a problem where there are a lot of air-conditioners and such, whose motor controllers don't have a low-voltage release