Current behaviour is that you start to watch a conversation as soon as someone mentions you in it. As a result you get all future comments and e-mails in that thread delivered to your inbox. I feel this should be a personalizable setting, so that auto-watching when mentioned can be enabled and disabled by the user.
The reason is that users that get mentioned a lot and asked for input on e-mail drafts now get the entire conversation in their inbox even though they're no longer needed by their co-workers. This creates unnecessary clutter. If for some reason the user wants to follow a specific conversation s/he can actively select to do so by setting 'Watch this conversation' manually if the auto-watch feature has been disabled in settings.