One of the features that we have added between ARRv1 RC and ARRv1 RTW is host name affinity provider. This feature was designed specifically for shared hosters who uses the host name affinity feature in ARR to provide shared hosting services. (More info on the shared hosting using ARR can be found here.)
For customers who are using host name affinity, with host name provider feature in ARRv1 RTW, there are really two different "stages" of load balancing.
First, the host name provider is used to determine where the new host name should be affinitized to. ARRv1 comes with 2 providers out of the box (Microsoft.Web.Arr.HostNameRoundRobin and Microsoft.Web.Arr.HostNameMemory). Because it is using a provider model, a custom provider can also be added.
Second, if the host name is configured to consume more than one server, the load balance algorithm is then applied to determine where to forward the request among the affinitized servers that have been determined from the first step above.
(Previously, with RC release, both steps above were using the same load balance algorithm. The change in RTW is that we are now using the providers for the first step.)
To see the benefits of this feature in ARRv1 RTW, review the follow blog post for more info.