This is only necessary if you activate wifi calling, which (at least in my case) is disabled by default and demands an address upon activation.
Without that, 911 calls are placed through traditional mobile networks where your signal is triangulated to provide your current location.
Wifi calling uses VoIP and doesn't include any location data so it must be manually provided.
You should be giving the address to the 911 operator you're speaking to anyway; location data from the carrier is only necessary/useful for things like calls that immediately hang up (maybe you can't actually talk due to danger, but manage to get a call out for example), or when you're too incoherent to get an address out of.