Emergencies......................redundancy. Chief
We have 3 hand-held VHF radios plus a mounted unit below with an external cockpit mic. One, my wife carries, one stays in the cockpit when travelling, and the third--the newest one w/GPS & DSC--stays attached to my belt when I'm working the boat. Now, I keep it turned OFF (and fully charged) after learning how fast the battery drains on a GPS hand-held VHF. After all, it's not that much good to you if the battery charge is near its end when your emergency arises! On my last trip (still in progress) the cockpit mic went dead. Sure, I'll probably fix or replace it but how nice to just switch to the hand held for monitoring and for voice contact from the cockpit. Who do I talk to when cruising not in the company of other boats? Well, we don't have many bridge tenders along the CA coast (b/c there is no ICW), so it's Harbor Masters/Police or dockmasters, depending on where I'm arriving. Sure, now with cell phones, we do a lot of communication that way as well.
I've always have one (but now sometimes two; one the GPS unit which is switched off) in the dink when using it offshore at the islands. If I don't have the second VHF in the dink and I'm alone (wife on the boat), I carry a walkie so I can still "ring her up" on the mother ship if there's an issue, etc.