Eg My landlord requires a yearly form stating my locker #. Of course I would lose any record I tried to keep in my own papers, so I have to visit the storage room to get the #. If I had the ability to add the # , as a 'comment to myself' to email I could just look back through my saved emails.
Eg I lobby for changes (eg to tax forms, etc). It would help to keep track of who was on board if I could note beside each mail "ignored'" or "passed" or "yes" or "no" or "the # of the correspondence history".