Garry Bargsley shows a use for extended properties on databases:
Databases listed with 1, 2, 3, 4? What do those databases represent? Where did those databases come from?
Would you believe me if I told you there was a way to identify where the databases were sourced from?
A setting that can be used in SQL Server would allow the person who built these databases or restored them from another system to add a note.
Extended properties are very useful but also very easy to forget and difficult to manage. I’ve seen a few vendor products make great use of them but in-house development tends to ignore them.