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

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

Since atheism isn't 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.

That said, some people stay in church because of the community support, like daycare or other assistance. It's not that these people are strong believers... it's more a question of practicality, and not wanting to sabotage their lives; they stay in church.

Atheist and humanist groups have been working to provide family services, so this demographic of church-goers has more options, and won't be trapped in a place or worship forever.