Answer:
I'm a 100m sprinter and I would say that it really is vital. Coming out of the blocks with power is the most important part of the race, because when you are ahead, you dont exert useless energy, but when you are chasing somebody, your body will tense up and you will be fighting to make up lost time.
Coming out of the blocks takes alot of leg strength.. the first 5 steps out of the blocks need to be low and you need to put as much force into the ground as possible, it will allow you to reach top speed the fastest.