At the moment as soon as you make a change to an issue an email is sent to the Reporter, Assignee, and any Watchers. It is common that someone will make an number of changes in quick succession ie change assignee to themselves, add a comment, and then mark issue as complete. This will send an email per update.
It would be preferred if, after the issue is created that the notification emails compile a number of the updates over a defined period of time (could start at 15min) and submit to the distribution list (as it currently is) in a single email.