I use it all the time. But even so, I don't use it enough, because again and again I kick myself for not having set it up (i.e. not having "saved" a particular location).
Two things it's particularly useful for:
(1) My commute is a lovely and quick jaunt across a few parkways -- traffic permitting. Which often it doesn't. When one of them is jammed, you want to get off and do sort of a diagonal end-run to some point on the next parkway. Which isn't easy around here, because it's impossible to
know all those side streets and alternate roads. They aren't laid out in any kind of easy grid and a lot of them are blind alleys. It's really kind of a maze. (Pretty cool, eh?) What I've done is, I've "saved" some of the key spots in each next parkway, so wherever I get off, I can plug one of those spots into the Nav, then tell it to find a "Minimize Freeways" route, and it finds the best "end-run."
(Sheesh, it's a lot easier to do than to describe.)
(2) Forget it, I don't have it in me to explain the other one.
