When a watched issue is updated, it would be very useful if the subject line could indicate the type of update, i.e., whether a worklog has been added, a comment edited, or whatever:

[JIRA WorklogAdd] (ABC-22) Users cannot X with feature Y enabled
[JIRA CommentEdit] (ABC-22) Users cannot X with feature Y enabled
[JIRA FileDelete] (ABC-22) Users cannot X with feature Y enabled
[JIRA ScreenshotAdd] (ABC-22) Users cannot X with feature Y enabled
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.
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This would be a great help when working through a list of email notifications, since the list would be much more informative, and depending on the watcher's role, reading the subject line alone would often be sufficient.