The "count member replies recieved" option at Admin Panel -> Settings -> Switches allows you to keep track of how often people post on the topics of a member. It sums up the total number of posts on all the topics owned by the member, and makes that total available to display with {MEMBERREPLIESRECIEVED} wherever you want it (by default, it shows in the View Profile page).

Enabling this option slows down post submissions slightly. The effect may become significant if you have hundreds of thousands of posts.