During archive-style transaction logging, this setting automatically cleans up log extent files over the number specified by this setting during runtime, instead of waiting until you perform a clean shut-down and startup of the Domino server.
The default value is 65.
There is no recommended value.
You should set the value to the normal extent working set size for your server. For example, if you normally have 125 .TXN files in the transaction log directory, you should set TRANSLOG_MAX_ARCHIVE_EXTENTS to 125. Then, any time the transaction log archiver has not run for some reason, on its subsequent run, the extents will return to your normal number of 125.
Lotus Notes/Domino 8.5.1