The GPS with a map can come in very handy.
I have a friend with a Garmin 705 and, on a rally, a group missed a turn and got really, really lost.
He pushed the "return to start" setting and the GPS took them back without a hitch.
You can also preload a route into the GPS and it will tell you every turn ahead.
My opinion:
I have a 605 and a Vista. The Vista is cheaper and works much better and is more useful than the 605.