Theology in the literal definition is the study of God. Used more commonly as the study of religion, or the study of God in relation to the world.
Theology is used to better understand God. If we better understand God, we can better understand what His will is. And if we better understand what His will is, then we can better align our wills with His.
Theology for someone who does not believe in God might be good to understand the concepts of God. Of course, only an open-minded non-believer is likely to involve himself in this. So, a real atheist might get into theology to seek knowledge of what God is, if there is one in their opinion. The modern atheists (or “new atheists”) wouldn’t be so open-minded, but would rather use terrible arguments and name-calling to boost their egos.
EDIT: Also, if Jesus is the Way, the Truth, and the Life, then by studying and seeking out the truth, you are knowing the Truth better and better, and therefore knowing Christ better, which is what he wants us to do.