[sciurus]

Because when you treat those three aspects of scaling as dimensions of a cube, you can visualize what it means to scale on different axes.

See this diagram http://akfpartners.com/techblog/wp-content/uploads/2008/05/a... taken from http://akfpartners.com/techblog/2008/05/08/splitting-applica.... For in-depth discussion, see the book The Art of Scalability.

http://theartofscalability.com/