Used to track a vehicle when stolen or could be via the internet, should be a key on them so you can go to the website put the key in and you can see where the car is usually to 10-15m of where the car is, what speed etc..
or if other type the police use a special aerial to locate the car, not as good as need to now the location so if car is far away chances are alot lower
but if it has it when it was first imported chances are 1 it will be japanese and 2 will still think your in japan so very doutfull it will still work correctly
and to get insurance reduced you would need a certificate or take it to someone to check it over and verify it works etc.. to then issue you with a certificate to proove to insurance that it works
cost normally £100 to have this done on alarm not sure on gps unit
hope this helps