JSR179 allows a device to have multiple location services. For example, a cell phone will often have a coarse-grained location service based on trilateration of nearby cell phone towers and a fine-grained location service that uses an internal GPS chip.
Trilateration is good for cheap location determination, because as long as a cell phone is "on line", it's already talking to the towers on a continual and periodic basis. However it doesn't work if there are no towers in range (or not enough towers), and the guaranteed precision is only 1 km.
GPS is much more precise and works in places where cell phone service isn't available, but the GPS circuitry consumes so much more power that some phone companies actually made it unavailable to all apps except the built-in emergency dial system (911/999) on many models.
JSR 179 permits basing the choice of which location service to use via abstract decisions about power usage, precision, and so forth. This keeps it from having to know specific details and allow other options, such as adding a third location device via a USB plug-in, for example.
If you need a rough idea of where you are on a continual basis,
you should ask for low power, low-resolution. If you need to have a more precise location, as for high-resolution services. It depends on the app.