VU hit it on the head.
Let me add that session_connect IS what makes a MMO*. Without it, you'd be limited to having ALL your users in one level or rather in one machine. This will kill system performace and game performace if like VE said, you go much more beyond 20 ppl with no optimization. You could double or triple that number with some easy opts., but you'll still never hit or exceed 100 users.

SEssion_connect allows you to distribute your load across diffrent zones and thus diffrent servers and ever diffrent computers; critical for a MMO*.