When the „Pro Performance“ add-on is enabled, the post and thread counts are fetched from a cache which requires much less server resources than the default real-time calculation.
The cache is a database table that contains the post/thread counts of all users. It is updated once a day by default (on 2:30 am in the 1.0.0 release)
After the installation
Note that right after the installation the cache will be empty. So there won't be shown any post and thread counts for any member. You can update the cache manually by running the corresponding cron entry (Tools / Cron entries). However, keep in mind that this will calculate the post/thread counts of all members! So you may want to do this when there is not much traffic on your forum..
Note: This add-on requires Post Areas 2.0.x