Sure, you can't have much runtime, but if you got like 15 minutes for each device and it always worked, you could smooth over a lot of generator problems when something chews through the building's main grid connection.
Did lose one building about 20 years ago when the generator didn't start
But then I assume that any services I have which are marked as three-nines or more have to be provided from multiple buildings to avoid that type of single point of failure. The services that need five-nines also take into account loss of a major city, beyond that there's significant disruption though -- especially with internet provision, as it's unclear what internet would be left in a more widespread loss of infrastructure.