Now, you may say that this is totally counter-intuitive, as if you have a Wi-Fi signal, what do you need 4G for? But (and please correct me if I'm wrong) 4G is not just for data, but also for voice.
*If* that is true, if you are connected to a Wi-Fi hotspot, hopefully not all of the battery life will be sucked out of your phone through data-centric actions that your phone does, as it should be delegated to Wi-Fi. At least that has been my experience.
Then you could turn on 4G because that would increase the chances (I think) of my phone calls actually staying connected while I talk in my apartment building in Bay Ridge, Brooklyn.
If this makes absolutely no sense, just tell me so. Otherwise, let me know if you think it would make sense as an enhancement request for the Galaxy Nexus for some future update.
Thanks