Excellent slideshare by Andrew Rusling.  I would recommend that anyone wanting a view read The Phoenix Project http://www.amazon.co.uk/The-Phoenix-Project-Helping-Business-ebook/dp/B00AZRBLHO, followed by The Goal, Theory of Constraints http://en.wikipedia.org/wiki/The_Goal_%28novel%29

The latter is not set in an IT environment. But the same principles apply.

[slideshare id=46627458&doc=tocandqueuingtheoryslideshareversion-150403201531-conversion-gate01]