I was raised as an atheist, but explored different belief systems as I grew up. When I found out that there were others who did not believe, and they had a name, I felt like I had found my people. I learned much more about Christianity and science. Now, I no longer feel like I'm missing something, I do not apologize for not believing.
One of the most profound effects has been that I'm no longer dependent on anti-depressants. I believe this is because outside of religion, I can live a congruous life, but inside religion I had to live like things that were completely illogical were logical. Now I wonder who can live a life like that without being depressed!
The funny thing is that all those religious sayings now truly apply to me: "I once was lost and now I'm found!" "I saw the light!" "Free at last!" "I've found the peace that passes understanding!"
It's an odd (old) and interesting question.
Admittedly, I don't see how atheism has changed my life. Perhaps because I was never religious to begin with? It's a type of question which seems to say more about the question than the answer. Atheism can't really change your life in any way, it's like learning to live without krill. If you seek answers in atheism, you'll be sorely disappointed.
Gave me a rash.