Even within very small farms being able to distribute the workload in your farm across more than one server makes great sense. Within Citrix XenApp 6.5 we ass load evaluators to servers using group policies. Two load evaluators are provided as standard: the default and advanced.
The default evaluator looks at users connected to the server; the advanced look at CPU, MEMORY and page swaps. Both include a login load throttle rule to prevent to many simultaneous logins to a server.
We can edit the system supplied load evaluators but we can copy them or create new load evalutors from scratch and include our own load evaluator rules. These rules range from IP Address to Schedules as well as more traditional load rules such as disk IO.