Chris, you'll find the debates on that here at TBN as exciting as the sudt/udt or dino/sythetic oil "conversations".

No, it isn't absolutely necessary in the summer, if you have great fuel. The problem is that in some areas of the country, there is not consistently good fuel and some areas mandate this and that (bio) be added for political reasons.
Kerosene and snake oil, many guys call it. Good insurance others claim. You are gonna have to make up your own mind in the end. An ounce per 3 gallon can? It won't break your pocket book. The winter? Given the number of gelled fuel filters reported here at TBN last winter, well, you'd get a lot of support for the idea. Do I do it year around? Yes, I do. It's my tractor and I am old enough to make my own decision.