For example, a conference announcement might contain:
Scheduled: Invitation: 1 Aug 2008 17:00 -0400,
Warning: 1 Sep 2008 17:00 -0400,
Event: 8 Sep 2008 08:00 -0400,
Expires: 12 Sep 2008 16:30 -0400
This could indicate that the invitions must be accepted by end of business
1 Aug, papers are due by end of business 1 Sep, the conference starts at 8
am on 8 Sep and is over at 4:30 pm on the 12th. (One might also infer that
the conference will be held in the US Eastern timezone.)
A MUA could be configured to change the color highlighting of the subject
listing for each of these intervals and perhaps archive or delete it when
the conference is over.
One advantage of this is that I doubt that any backend systems will try to
interpret this field and do something unwanted.