It's like jlouis said, with Erlang you have to kill your processes off when you've finished with them and if you don't they leak. In Pony that's done for you automatically.
Thanks, I think you end up killing your Erlang processes most of the time because this is the model you follow when programming in Erlang. Using HTTP as example, while in other systems it is a really bad idea to have 1 req -> 1 process (or thread) mapping in Erlang it is encouraged. When the request is answered and the response is sent back the process dies. I think is a fairly simple model. I guess I need to look into Pony more to understand the importance of this in it.