In SharePoint 2010 the user login token is stored in the memory of each web front-end servers (WFE). If load balancer is configured to route requests to the WFEs and if a user request goes to a different WFE than his earlier request then the user will have to authenticate again. In order to avoid this multiple authentication and delay, sticky session (server affinity) is configured with load balancer.
In SharePoint 2013 the user login tokens are stored in the new Distributed Cache Service and are available to all WFEs, so it is not required to configure sticky session. This solution is more scalable and reduces memory utilization in WFE.