I live in California. Pollsters are 100% confident that Obama will win all of our electoral votes.
My daughter lives in Texas. Pollsters are 100% confident that Romney will win all of their electoral votes.
So while it is irrational, I closely follow the presidential election and know that many of my friends in these states do as well.
It's a tribal thing, apparently. My rooting for the Giants to win won't change their odds in the playoffs. Yet I pay attention. I root for them to win. I want the Giants to win.
So partly we vote and cheer for "our team" politically because we think our vote will make a difference. Probably more importantly, we do it because it makes us feel - for whatever misguided reasons - like we're not alone in our worldview. We're together in the stadium and we can hear others chanting the same slogans.