They gonna carry around a file of thousands of places as they gear up heading to the call? I stand behind it being unnecessary nonsense. I could see it for a school, hospital or large church but not everyone.
... well, YES! at least the Fireman at my last inspection in Colorado 15 years ago did... I used to hate and dread when the FD would make their surprise visit... However, that last time in CO, a newer Firefighter and I got talking and I was able to see it from his side - (this was not from what was legislated, or whatnot, just one person trying to do his job the best he can)... well, the long story short, he said they get city map of the buildings, all digital and only a few minutes - basically when he runs into a burning building trying to save someone, he wants to know exactly where things are in the shop - makes a lot of sense to me.
Talk to any firefighter and ask what was on their test... they have to study a map for something like 10-30 seconds, then accurately answer questions about the layout - how many rooms, where are they, can you draw a rough layout from memory, etc. This is because they get the maps.... Now, how much use the actual room number signs are in an actual emergency is up for debate - but having a relatively static layout with common room numbers they can refer to probably makes their job much safer overall.
Imagine a fire chief asking where people may still be in the building: "... they were in room 135.... no wait, 112, no it was room 7,... dang! no we made it a closet now and there is no number.... oh, no its conference room 2 now..."