It is not really meant to monitor all of the changing road speeds. You can have up to 10 speed zones. These zones can be set for school zone where the speeds change down to 15mpg from 25 sometimes. Or other zones.
A use for this would be if you borrow your car out to someone. If your speed limit is set to 75mph (because you dont want them going that fast) then it will remind them to slow down and thank them when they do.
Of course if you dont want to here it, you can set a speed zone to 100mph and it wont even bother you again, unless you go over 100.
Also this will announce when you are approaching your home and run an RR command once you arrive. This is usefull for internet updates or what ever you want to happen when you get home. It does the same thing when you pass through a zone, it will run a command for that corresponding zone.
So if you want your computer to update at starbucks wifi, then you could have it run a command to do so.