Why do people take anti-depressants?

I know from personal experience, anti-depressants can really be wonderful for some people, stress the word some....its like everything in life, some things are great for some people...and some things arent. anti-depressants helped a very good friend of mine, he is like a different person, its great. I took a mild depressant awhile ago and it was horrible, it made everything worse...I am on the fence with antidepressants, I think they are good, but they arent great either