One of the benefits of using the WCF-Custom or WCF-CustomIsolated Adapters is the ability to specify a Custom behavior. A Custom behavior acts as an interceptor and can be used in both Receive and Send scenarios. If you are not familiar with custom behaviors, you are probably wondering why they exist since we have BizTalk Pipelines. Remember, WCF is not a technology that is exclusively used by BizTalk. WCF can be used outside of BizTalk and therefore Custom behaviors benefit non-BizTalk Solutions as well. The ability to intercept messages as they are being received or sent is something that other Web Service technologies do not provide. So having this capability is one reason to use WCF Adapters over the classic SOAP Adapter.

Once you have compiled a custom behavior and placed it in the Global Assembly Cache (GAC), it now needs to be registered. In WCF applications that do not involve BizTalk, Custom behaviors need to be registered inside the server's machine...