Studying Exchange 2013, found something worth sharing :- An important change that is very important & is different from previous version.
No more Layer 7 Load Balancing (you can use it but not required), yes you heard it correctly No Layer 7 Load balancing requirement.
Layer 4 Load Balancing can be used & HLB configuration complexities can be avoided.
All of the user session information is now maintained on the Mailbox server Role. CAS truly acts as a proxy & thus no need for requests to maintain affinity.
In Exchange 2010 if the request doesn't go to same CAS, User experience is impacted.
if you want to go in depth, refer below link: