Lack of adequate sleep has a real and measurable impact on our cognitive functions and emotional regulation. In addition, lack of sleep depresses our immune system, raises stress levels and, correspondingly, blood pressure.
Even worse for anyone on a diet, lack of sleep wreaks havoc on our appetite and metabolism of glucose. Run yourself down enough and you'll be at risk of developing pre-diabetic symptoms.
Finally, that old adage, "let me sleep on it", really is true. While you sleep, your brain is hard at work integrating the day's learning, mapping new ideas with existing ones and making the critical connections leading to new insights.
Bottom line? If you're in a demanding role requiring clear, calm, rational thinking, then lack of sleep is not an option: build in a good night's sleep. This one you cannot fake- your body knows and reacts on its own when you aren't getting the sleep you need.