After testing it in a limited rollout, Google has officially unveiled "WiFi only" mode for Maps on Android. When enabled, it will keep the app in offline mode, blocking it from using expensive or spotty cellular data. At the same time, messaging and other apps can still connect to mobile networks. That will help travelers cut down on roaming charges, as navigation is often the only reason you need data on a trip. It will also be a big help to folks with limited data plans.