[happytoexplain]

As far as I can tell, the parent is asking the even simpler version of this question, which is "why not just store everything as a Unix timestamp", so even just the obvious example suffices:

I set a 9:00am alarm and then move to a new time zone.

If they meant "why not store everything as a Unix timestamp after pencil-erasing the time zone and replacing it with +0000", then you'd need the more complex example, but then the reference to GPS wouldn't make sense.