What does it mean if a server is off the load balancer? [closed]

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http://serverfault.com – I have heard people say "oh that server is off the load balancer so you can run that expensive script on it". What implications does a server off the load balancer have? Fundamental to answering this, I understand load balancing, but I don't know what the dynamics of a system with 5 servers (4 on the load balancer) has. Thanks (HowTos)