I just noticed when I picked up my Nexus from idle (it was on the table with screen off) that it was back in 3G mode then quickly switched to WiFi. I never noticed such behavior with other android devices I've used. Is this a setting issue that I need to change? When I am home and on WiFi I really dont want the phone switching to 3G/4G when it's not in use....unless there is some advantage to that?
I think it's better for battery life to have the wifi off during sleep so that the phone is not constantly searching for networks to connect to, especially if you're not at home. However, I had an issue with the wifi re-connecting after waking up, so personally, I just leave the wifi on all the time.