I think it would be really great if most admin settings could have a notes area.

Similar to the (?) help icons beside settings it could pop up a little area where you could justify each change in rich HTML and maybe link out to an external issue/tracker system.

It would be great for auditing (in a similar sense to the existing configuration change log) and provide a way for admins to justify why changes are made.

One area I'd particularly like to see this in is rule builders for audiences etc. eg. "I[admin name] added this rule on (date X) to cover (issue X)[linked to tracked issue]" sort of thing.