I've explained it to you several times, but I'll try again with an example:
Say someone is a theist... a Christian, specifically, say. Because of his theism, he tithes 10% of his income and spends 2 hours a week in church.
One day, for whatever reason, this person stops believing in gods. Because of this, he no longer has the justification to tithe or spend time in church and therefore doesn't. He now has 10% of his income and 2 hours a week that used to be spoken for but isn't any more.
That 10% of his income and 2 hours a week can be seen as a benefit of his atheism. He no longer has to incur this cost that he was incurring because of his theism.