Distributed CAS Servers in Remote Sites

Hello

I cannot find any documentation on the best practice or recommendation for deploying a CAS role server is remote AD Sites.

All Mailboxes will be held in Site 1, with CAS Servers in Site 1 (either multi or single role servers).

We have 50>100 Outlook 2010 clients in Sites 2 and 3,  that will connect back over the WAN to Site 1 for their mailbox data, would there be a benefit to Exchange or the Outlook Clients in Deploying CAS Servers in Sites 2 and 3?

I believe that a CAS Server is sites 2 or 3 will proxy to CAS in Site 1 and then proxy that request onto the Mailbox Server hosting teh active copy of the mailbox in site 1.  If we do not deploy CAS in Sites 2 and 3 then the Outlook Clients will connect to the CAS in Site 1.

Thanks for any input\advice.