It only works in some instances like if your running in a marathon.. start off slow and steady and you'll have more energy in the end to finish the race hard rather than those who start off giving it their all  right away, their too exhausted by the end of the race to keep pushing and giving as much as they had at the starting line.
but in other situations like a short race you don't want to think slow and steady, or you'll find yourself in the back of the line.