That's a great post! I remember reading that.
The thing to remember, and not lose sight of, is "What am I trying to accomplish with this workout?" Always ask yourself this before you do anything, and it will save you a bunch of wasted effort, as well as time. The body will adapt to the largest strain put on it in a workout. If you have a "mixed" type of workout, you really end up shortchanging yourself. The body's energy systems do overlap, so you will end up training at least a little of each aspect of your physiology no matter what you do, but there should be a clear cut mission to what you are going to do each workout.
That mixed type of workout is the gym equivalent of "junk miles".
Also, to put the stuff Taras wrote in other terms: You don't train for Kilos by doing Kilos. You don't train for Flying 200s by doing Flying 200s. I've seen people do this and, as Taras put it, they were shortchanging themselves.
I like to use the Karate Kid analogy with training. For best results, train things in components. All of the components come together on race day. That's what Mr. Miyagi did for Daniel.