It sounds to me like you are asking for the advatages between invoking WCF SOAP services and invoking WCF HTTP Web services. WCF SOAP services add additional features (like security, reliable messaging, etc) but require SOAP clients (and larger message payloads).
WCF HTTP Web Services can be called from any web browser or application that can make HTTP requests, but it does not provide security (unless you use HTTPS) nor does it provide reliable messaging.
I hope this information is helpful,
WCF Documentation Team
Marked as answer by.NET DevSaturday, March 10, 2012 2:24 PM