Our problem is that we get to many E-Mails from Phabricator.
The reason for that is that you get subscribed to a task if you write something in it(picture below) by default.
It is common that we need just one piece of information from someone in a big task.
E.g.: boss needs to give his "OK/Go" in a software or hardware project.
After his answer the person is not interested in the task anymore but now gets all E-Mail, notifications and discussions from this task.
We think it would be the best solution if subscription would be optional.