Once in a while people get tired. This may not have big effects on your overall life. But if you get tired too often, you might lose precious sleep and develop an irregular circadian rhythm. This would ultimately affect your life, including your work, and productivity.
If you come to work tired, you might find it hard to pay attention on things. This is very dangerous to your productivity, especially on your long-term projects. Without proper focus, a meeting would be detrimental. You might even fall asleep while someone is presenting an important point.
Make More Mistakes
If you are too tired, you will lack attention, concentration, alertness, problem solving skills, and good reasoning. You don’t want to commit too much mistakes in your work in a day.
When you are too tired, you will lose some of your motor skills since you are close to falling asleep. This will make you prone to accidents. This will jeopardize not only the profit of the company, but your life as well.
Being severely sleep deprived can lead to high blood pressure, heart attack, obesity and stroke.
With all of the bad things involved in being too tired, you are giving your boss a reason to fire you.