Recommend adding guidance to each of the channels in their introductory paragraphs about "when to use". REST: describe as the primary channel type developers should consider, for broad compatibility. This is due to the familiarity of the protocols (HTTP/s) and general usage in FHIR. Websocket: describe as useful for connected clients which cannot expose an HTTP/s listener. Email: describe as useful for non-client applications (e.g., there is not a FHIR client running on a device waiting for notifications), public health applications, etc. FHIR Messaging: describe as useful when a system has invested into a messaging paradigm.