-Why Is It Useful?
The reason why this is useful, because it will give a warning to prevent the database from growing to 64 gigs. Or, prevent the database from becoming corrupt.
-Who Would Benefit From It?
This would benefit anyone, Domino Administrator or enduser, from having a corrupt database due to size limitation.
-How Should It Work?
When the database reaches 50 gigs, a message will be wrote in the logs, local and server, stating that the database has reached 50 gigs and should be decreased to prevent the database from growing to 64 gigs.
Also, when opening the database, an informational message will either be mailed to the Admin, if the database resides on the server, or the enduser, if the database resides locally, stating something along these lines:
Database, database name and location, has reached 50 gigs. Please run compact against the database and limit the number of documents in the database by creating a new database without documents. Then, start creating new documents within the new database.
https://www.openntf.org/main.nsf/project.xsp?r=project/Mail%20File%20Digest/summary
is probably going to provide what you are looking for.
Note that in V10, the database limit is now 256Gb