Its only the GPS units that are combined in some way with transmitters that can be turned on to track things. So, for example, almost all GSM cell phones (which contain a GPS chip for e911) can be used to find its holder's location. Typically they also have WAAS so its accurate to around 3 m.
A $5 GPS dongle or a $50 PND sans phone does not contain a transmitter, no.
Parents like them because they can keep tabs on their kids. Bosses with workers too.
Even down to what products they buy at the store. (what aisles they linger in, etc.) Cell phone companies are making a lot of money selling that information. Soon people will use them like money. You'll just take products out of the store and they will be automatically deducted from your account, no checkout necessary. They are already doing this in EU and Japan/Korea. We are around ten years behind.
Google "location aware services" or "location aware"