Reduces database size and improves performance. If you feel forum performance is going down a bit, do it, or after doing something like topic archiving.
compacting will only help if you have deleted lots of stuff in your database, compacting after an archive won't make that much difference since you are not deleting them.
compacting will only help if you have deleted lots of stuff in your database, compacting after an archive won't make that much difference since you are not deleting them.
When you archive you delete topics and replies. If you do not compact, the free space at those tables won't be reclaimed.