This question sometimes comes from theists trying to ask why they ought to be atheists. It is as though atheism is some kind of service/club, and they are asking why they should give up their current benefits package and switch services to yours. It is like they are asking:

"Why should I switch phone service from Theist Cellular to Atheist Cellular?"

Since atheism is not a club or religion, or anything like that, there's no "benefits" to be gained per se. Although, if one adopts critical thinking and skepticism, it can improve one's decision making process in life.

The reason atheists are atheists are because they tend to care that what they believe is actually true; not because it feels good, or is comforting, or are frightened into it.

The reason one should be an atheist is because the god claims have not been proven.