A question was recently raised about Localizer service and it's affect on battery life. Localizer service has a VERY small impact on battery life. That's because your GPS device ALWAYS produces GPS data, regardless of whether or not anything is using it. You can't turn the chip on or off. When data is available, the chip driver produces an event. If an app needs the data, it subscribes to the event. so an app doesn't "ask" for data, the chip "tells" the app there is data available and the app can then use it.
Another way to describe it is that Localizer, or any other GPS app doesn't "pull" data, the GPS chip "pushes" data. So yes, there is a slight amount of overhead with the service version because it places a minute load on the CPU, but it does not force the GPS to stay on (its always on) or cause the GPS to work harder. The GPS works the same all the time, no matter how many apps are connected.
Note: The GUI version of Localizer have a somewhat more significant impact on battery life due to its rendering of graphic information to the screen. Although very small, it is still enough that it will increase your power consumption slightly. We do recommend turning Localizer 5 GUI off when not in use.