Purpose of WCF mocking

I am having difficulties while trying to understand the purpose of mocking my WCF applications in unit tests. I have read this article Testing with mock objects and I believe I got the idea why we use mocking in standard application - it is better to test behaviour rather than implementation of the method. So with using Mock objects, I can test whether certain method called certain mock object, whether it changed some properties etc.

But while I was searching for some good ways how to test WCF, everyone was suggesting to use Mocking as well. The thing is, that I feel like I should test whether method (which is communication with service) is really able to reach the service and obtain result, that is satisfactory...which is not the case I will achieve using mock object.

My question: Is using mock objects in my WCF app unit tests really intended to test only whether the method tried to call the OperationContract(method) exposed by service (while not expecting the real results)? Or am I missing something?