People have asked again recently what the difference is, so I found a mobile your speed is setup and did a few runs to compare.
K band, Constant On, BIG sweeping curve, PSL 35 mph.
Highway mode, approx 25 seconds warning, 1/3 mile range. Autoscan mode, approx 20 seconds warning, 1/4 mile range.
As you can see, at 35 mph, you have more than enough time before reaching the target where the officer sees you, by that time the RD is pegged at full strenght, so gotta pay attention to your RD and not dismiss as a possible false. BUT, if you are talking about 70 mph around a bend, you will have very little time! So even 1 extra second can mean the difference between getting a ticket or not getting a ticket.