Serves no purpose compared to a modern phone with inbulit GPS or many tablets. A modern smart device can receive GPS, Glonass, BeiDou and likely Galileo simultaneously. You'll often see 20+ satellites (from the various systems) being used for position fixes. Extremely fast position acquisition and plenty accurate (for offroad use).
In the 'olden' days, it was common to have an external GPS puck, either wired or that Bluetooth connected. These were useful for use with a laptop since then and even now, they are typically gps-less. But now a tablet with expandable external flash storage can hold maps of an entire country and even a whole bunch of high res aerial photograpy. Plenty of quality and low cost apps to provide the navigation ability, either street, topo, aerial etc.
cheers,
george.