That all depends on your goals in life. People like Bill Gates are (to put it mildly) competitive assholes; their only goal is to prove to everybody else that
They Are The Best. Money is just a way of keeping score.
Personally, I could easily think of many legitimate ways to spend several (as in 30 or 40) million dollars or more, but I would be quite satisfied if someone handed me a cheque for a single million.