When deploying BranchCache in Distributed Cache Mode (where the clients cache and deliver local content instead of a branch server) the theoretical maximum is 254 clients. Which is the size of a subnet using a 24bit mask. However, the recommendation from the Microsoft Product Group is to use enable it for 50 or fewer users. This recommendation can be found in the TechNEt Library.

The more clients that you enable Distributed BranchCache on the more Cache Discovery Traffic (bandwidth and processing power) is required used to keep the service status and data locations up to date. The service has been tested with around 100 clients, but at this point the Cache Discovery Traffic becomes too high.

At the point where a branch office has over 50 clients, adding a Windows Server 2008 R2 Print Server, and BranchCache Server should be considered. This will reduce WAN traffic and will reduce the Cache Discovery Traffic from the LAN. Also evaluate the other benefits a Windows Server can provide to the Branch Office.