If I recall correctly, Madison mentioned two things, that were reasons WHY they would run the generators.

1. to make ice.

What was the other? Was it to make hot water?
were there other things?

I'm wondering if the hotel has a natural gas supply.

 

I just checked... the comment was to run the generator a few hours a week, to make ice, and boil water.

They were to check cars for gas.

Seems unrealistic to me that a generator large enough to run a hotel like that would run on gas, and not diesel.

 

During a power outage, Hallways without windows to the outside that are typical in Hotels, and apartment buildings, have "cave like darkness" where you can't see your hand in front of your face, even during broad daylight, unless there is emergency lighting. I suppose that once they clear a floor of walkers, they can leave the doors open and some light will sneak out into the hallways, but at night... total darkness.

Stairwells.... total darkness.

In some of the scenes in the hallways, the emergency lights were a blinking orange/yellow.

Back up batteries for many will last less than two hours, maybe some will last for 24-48 hours.

MAYBE one could justify running the gennie to recharge batteries, but to make ICE? That's silly. The noise will only attract more walkers, and more people.
Regarding boiling water, maybe some of the homes in the area have wood burning stoves that they can scavenge.