Let me explain. Let's say I have 20 servers, each with identical configuration, now I need to login to each server if I want to remove a certain script from the list of available scripts. Or, if I want to perform an update right now (for example when you update a bug, and I don't want to wait for the auto-update).
with a cluster setup, I can have one master and the rest will be slaves, and all setting (list of packages, admin email, updates, etc) will be pushed to the slaves from the master.