But they are on demand now, at the stations. The ones roaming on their own are for the convenience of those who may not know where a pod stations is and they can just "hop on" where they want. I don't see what the problem is of ones running empty is. In some areas, if there weren't pods cruising by, it would be totally dead, without a soul to be seen for regions around.
That is how I discovered them. I was tired of walking everywhere to see SL. One day, a pod was passing and I hopped it. It was a revelation. I saw stuff, I found the rez station and more routes. I took one of the notecards that is offered when you sit and found there were tons of these routes. On ALL the continents. It allowed me to see and find things I never would have just walking. Things that I wouldn't have thought to plug into search. And things that aren't in search, like a group of Frank Lloyd Wright house replicas on someone's land that they had built themselves.
With all the walking, SL was getting boring as a newbie and I probably would have quit. The pods let me discover it and I knew I wanted to stay.