What it means for you
Message passing is elegant and network-distributed. So what? What does it buy you, the programmer?
Well, it means that your programs inherit those characteristics — they too can become network-distributed with far less work than on other systems. But the benefit that I find most useful is that they let you test software in a nice, modular manner.
You've probably worked on large projects where many people have to provide different pieces of the software. Of course, some of these people are done sooner or later than others.
These projects often have problems at two stages: initially at project definition time, when it's hard to decide where one person's development effort ends and another's begins, and then at testing/integration time, when it isn't possible to do full systems integration testing because all the pieces aren't available.
With message passing, the individual components of a project can be decoupled very easily, leading to a very simple design and reasonably simple testing. If you want to think about this in terms of existing paradigms, it's very similar to the concepts used in Object Oriented Programming (OOP).
What this boils down to is that testing can be performed on a piece-by-piece basis. You can set up a simple program that sends messages to your server process, and since the inputs and outputs of that server process are (or should be!) well documented, you can determine if that process is functioning. Heck, these test cases can even be automated and placed in a regression suite that runs periodically!