One use of tracking where you have been is so you can then use the track logs to add GPS data to any photos you take. Just requires you to sync the time on your camera to that on the GPS, record where you have been and use a bit of software to insert the GPS data into the photo's EXIF metadata. Really nice if you use software, such as iPhoto etc, that can use the GPS data to plot where you have taken photos on a map for you.
I used my 305 in my pocket to record pretty much everywhere I went on my holiday in Alaska last year. In the car, light planes, boats, walking – it recorded at all very well from my pocket.
Being able to draw red lines of where you have been in Google Earth is kinda cool as well. 🙂