To have easier editing options for adding users for 'Manage Fields' area
So when you add users who need to be notified for under the Manage Field area, if you need to make any changes to a sites user that needs to be removed or changed, it doesn't retain the original user(s) that still need to be notified. You can't just remove one person or add one person to a field. You have to start all over again.
You should be able to just modify the field. It's really frustrating.