I thought the GPS navigations systems were nifty, but could not justify spending hundreds of dollars for it. I've been driving for 46 years using my senses and maps and I've managed to find my house every time.
So, given a $500 gift certificate to an electronics store by my insurance company, I did some shopping. Don't need another HD TV, don't need any more stereo equipment. Happens that they had a Garmin for the same price as my gift certificate so it became an easy choice.
Simple to set up and use, I did it in the parking lot of the store in just a few minutes. My wife wanted to go to a store across the street at a shopping center and she was able to see the street address so that was the trial run. From there, dinner at a restaurant that I've never been to so I plugged that address in. I admit, I'd have gotten to it the old fashioned way, but it would have been out of my way compared to following the GPS map.
You really don't need one, but if you travel to different destinations in cities or areas you don't usually travel, it certainly is handy. You can choose many options, such as the type of vehicle (I'm guessing trucks may get different routing), avoid tolls, avoid highway, shortest, fastest, etc.