One guy sends a message to three collegues. Two of them have own comments and used "reply all" feature. Just imagine how many threads will be stored in each inbox.
This is the situation that leads us to inbox overloading problem.
Get rid of broken context. Track messages about the same subject at the same place.
Rizzoma is a sort of continuation of wave, which is - in my view - one of the most important developments forward in human collaboration since the invent of the speech :)
The thing is that you are writing and creating a document, dialogue, etc *together*, where all are responsible and part in what is happening, and where order appears out of increasing effort and inputs. I.e., unlike a forum or something like that, here you have a document and discussion that ends up in more and more structure and insights by itself. Self-organisation - one of the most beautiful phenomena there is :)