Currently, when a user is assigned to a notification scheme, he or she would receive all notification they have been associated with.

The only way not to get notified is to ask the JIRA Administrator to remove them from the notification scheme or if they were watchers, stop watching the issue itself.

The reason for wanting to opt-out is due to how chatty JIRA notification can get at times and being able to selectively opt-out of notifications by having JIRA add a link to emails sent to them which they can click on should they want to opt-out of notification for just that particular issue.

This way users do not get notified too frequently and they can control in more details what notifications they want to receive and for which issues they'll like to receive notification from.