Reliability—Remote connections are not only slow, but they are much less reliable than a local function call. When a procedure calls a subprocedure inside a single application, it’s a given that the subprocedure is available. This is not necessarily true when communicating remotely; the remote application may not even be running or the network may be temporarily unavailable. Reliable, asynchronous communication enables the source application to go on to other work, confident that the remote application will act sometime later.
