I sometimes have to logout and login again to be able to kill wild 
threads of Icedove which survive in a blocked state after the windows 
have been closed. The idea to be able to kill all processes started in a 
session is not a bad idea. Corbet explains this very well and also says 
the idea has been around for many years.

     The decision to impose this on everybody has been taken by the 
Systemd team, and their fans now protest. I think they complain because 
systemd was hidden and it is becoming more and more visible and 
allmighty and it is obvious that whatever they do, they do it by its 
permission.

     Otherwise, I like the idea to have a better control of what 
survives a session.

     Didier