Originally Posted by Cone Wrench

It's more useful to think of a triple chain ring/10-speed cassette combination as a smoother continuum of gears rather than as a wider choice of gears. One doesn't really choose which gear to ride in, you just sort of end up in a particular gear as conditions dictate. The triple/10-speed combination gives you close rations in three different ranges and, of course, it is simplified, because in the smallest chain ring, you are only using the biggest two or maybe three rear cogs. Once you begin to visualize the gearing as single smooth continuous line, the advantages of the 10-speed cassette become obvious.