As mentioned above, historically, story-boarding was essentially all that was meant by Pre-Viz. Nowadays, Pre-Viz tends to mean computer generated, 3D animations, used to show the movements of actors, camera movements, props, sets, etc, etc. Just like story-boarding, it may be entirely unnecessary. You may not need either, but as scenes get more complex, you may want story boards. More complex still? Maybe a Pre-Viz would work for you.
Some of the best examples of this I've actually seen are on the extended editions of the Lord Of The Rings.
In answer to your question, Pre-Viz does work, but it's probably not necessary for everything, just like story boards.