No you don't have to let it guide you with a planned route. When no route in place, it'll show some very good info on the screen: your current position, speed, direction, the road/highway you are on, the nearby gas stations, restaurants...
By all means, go get a GPS device when the price is finally now down to $100 with maps included and ready to use right out of box.
James, former senior editor who does gadget review for CNET, was dead this time last year. Ironic, a gadget lover like him, did not have a gps in his car. When he was driving from Washington back to California after his Thanksgiving visit, he drove off the freeway in Oregon and got lost.
Only if he had a gps in his car, we won't have lost the greatest MP3 player reviewer.
It was that tragic story (fully covered by all the medias) made me want a GPS. I got two this year, one for wife, one for me.
Like you, I don't want the gps to find the best route for me (the LE and 3rd is still quite dumb on that), but it is a very valuable tool to help me to get to a unfamiliar place, such as garage sales. I'll never need to go to google maps and print some routes again. If I need to find a good route on google, I can just feed the route into my Tomtom. But mostly, I no longer need google.