The benefits are that you can become stronger and more energetic. Also good professional sportsmen earn a lot of money. The harms are that your health can become worse as a result of much strenuous exercise. Also sport is good for young people. When you become older, a more practical profession is much better.
I am fond of swimming.
I prefer to take part in the competitions if I am good at this sport. But as I am not a professional sportsman, prefer watching them.