Extreme Couponing

I understand the need save money and make cuts here and there, especially when it comes to the grocery store. What I don't understand is what people buy! To me when I see ads and coupons, it's for stuff I would not ordinarily buy, so I'd end up spending money to save money. I don't get that. I hear that some people donate what they purchase, or a portion of it, and again, I am spending money on what I am not going to use. The trend just fascinates and confused me all at once.