You have brought up a very good question that others probably have wondered about too. So its good to clarify here just exactly how that "Change Home" feature in Explorer Settings works.
By default, once the drone has locked on to the satellites in GPS Mode, the drone automatically sets that take off location to the Home Point as soon as its airborne. When initiating a Go Home command or you reach low battery level that triggers a fail safe Return To Home the drone will fly back to that starting point.
Explorer > Settings > General > HOME POINT > Options: Me or Aircraft
This "feature" is designed by the programmers to be used once you are flying. Based on your query it is not intended to be selected while your aircraft is still on the ground before flight. And as you can realize, there is no point to select Aircraft at this time since the aircraft has already established that spot for its default Home Point. And there is no reason to select ME before take off when you want the aircraft to return to your landing pad and not where the pilot is standing at take off. Logic prevails. (Yeah, Spock and I go way back!)
During a Flight you can go to the Settings > General > Home Point. Selecting MEat that time will transmit your device (cell/tab) coordinates to the drone for its new Home Point....providing your cell or tablet has LOCATION turned on to acquire GPS coords from the satellites. If you don't have Location available on the device or its not turned on selecting ME would fail to send a new Home Point as the lat/lon is not available. Beware! I assume the drone would continue to use the default Take Off location as its Home Point under this circumstance as a logical safeguard. You would have to fly the drone visually back to your new location.
If cell/tablet Location is On then wherever you are standing/sitting/floating is the landing pad for the new Home Point. I've tested this a number of times and its quite accurate. As Ansia mentioned, its used when the pilot location has changed from walking, boating, biking, etc. and you no longer want the drone to go back to the original starting point.
During a Flight you can also select AIRCRAFT for the Home Point. Wherever the drone is when you make that selection will be the landing pad coordinates for the new Home Point. Be careful when using that selection and be sure the landing zone is clear of obstacles and people especially if the aircraft is at a distance. I feel selecting Aircraft (location) during flight is something that would be used very infrequently and most likely only when the drone is in close proximity to the pilot unless there was a dire emergency.
As added assurance I just ran all this past Alejandro at Autel to make sure the explanation and programmer's logic was correct.