Hey,
I'm coming from redmine/chiliproject and one of the things I used all the time was the ability to toggle notifications. So if I'm just cleaning up some issues (setting versions, tags, etc...) I'm not spamming the crap out of my team.
I know I could just disable notifications temporarily, but thats a pain if all I want to do is assign someone an issue.
Another use case:
I've talked with my developer about a couple different issues in person, I got and create the issues in jira, and assign them... he will now get 3 emails... when he didn't need to get any.