Having a tracker is extremely smart in a lot of cases. If you have a very young child, it's always good to have the option to check where they are in case they get lost or worse. With a tracker in the shoe, it won't get lost and you'll have a sense of security. The same goes for pets that may head outdoors.
If going on a trip in a foreign country, you'll want to be able to find the others in your group even in crowded areas. Another good reason to have a tracker.