I hear what you are saying, and I have never worn one on a tour, but I am considering it for future tours for a few reasons. The main would be to stay conservative, and not go too hard too early and blow up later in the day. Since most of my sports tend to be high paced, I have to make sure I pace myself on tour. Another reason would be to tell when you are sick, or getting sick. You could tell this by your hr, and modify your day/days accordingly so that you don't push too hard, and pay later.

Obviiously I wouldn't be using the same way I use it training on my road bike, but I think there might be some practical applications for touring, and if you already have the technology.....