pointing to a approx. location on the map will help the GPS radio know roughly where you are as a starting point and will enhance time to lock. As you use the product and get an actual lock/location, A-GPS will be updated with more precise info. You don't have to touch it again unless you change locations by 150 miles or more while the GPS is off. For example, if you are driving and the GPS is on and functioning, it will be constantly finding/locking on to different satellites as you move -- no need to update a-gps. If you were to get in an airplane and take a trip of 150 miles or more, you should launch a-gps and select a new approx location to help the radio know again the best starting point for available satellites.