Maybe to clarify a little on what rebuild content does and how the comment counts/category lists work>

To save on performance server side comment counts and indexes of recent comments, blogs etc are built by an agent and the html is therefore prebuilt and stored and just inserted realtime.

If you use a local replica and replicate up to a version on a web server then it doesn't bother building these indexes it just sets a flag for thr web server version to pick up - an agent runs every 5 minutes to check the flag and builds the indexes if a change has been made by creating a new blog.

So the db can run across multiple replicas each replica has its own index (so the comment counts etc are correct for what that replica contains).

Therefore if you add content locally then replicate - the latest content or category list are not updated immediately - an agent runs every 5 minutes and if it detects an update from another replica it will update itself.

Rebuild content just forces an update of these indexes on your local copy and sets a marker for other replicas to do the same after replication.