To be honest 90% "it's fun to mess with". I had written my own looking glass type software with some historical statistics. I'm sure you could get similar data elsewhere but it was more about hooking into the route daemon updates and seeing general things or even watching what I was doing on other networks propagate live.

10% is having my own looking glass was significantly faster and easier for me to use. But I probably wouldn't have done it all just for that, it was just fun to mess with.