As quoted by the author, "I’m often asked by educators why I use wikis, blogs, AND Google docs. “Why not just pick one?”. The answer is because I use each in different ways. Each of these platforms can be used for numerous purposes. Here is how I use them."
I too am often asked why do I use all three. This authors post does an excellent job of offering reasons to use each one and they have also included several links to examples.
If you want a "60 second" answer to the question why use all three, read the article! It will be a well invested 60 seconds.