Bittman correctly states in How to Cook Everything Fast that mise en place, the practice of preparing ingredients ahead before firing up the stoves and ovens, adds time to the meal. That’s very true. However, I want to add that it also reduces stress. I like mise en place especially for recipies I’m unfamiliar with. It’s awful having things be boiling over while you’re trying to pestle out some pepper or chop an unruly onion, especially when you try to conserve electricity and heat.
My suggestion is: use mise en place while you’re learning to cook. It’s an investment in skills; once you’re familiar with the times every step takes you can recombine them into multi-tasking recipies, a la Fast.