Whilst I can see where the last two posters are coming from, I personally disagree with them both. Yes, food is fuel but, why shouldn't it be used as a reward? There is also some logic to the cheat meal rather than it being simply a reward.
The logic is that, whatever regime you stick to, your body will eventually get used to it, become more efficient. However, if you 'mix it up' once in a while like you do in your training, your body thinks 'hang on, maybe I don't know what is coming next all the time' and won't ever become too comfortable with your nutrition regime.
I have heard a number of stories about people overcoming a weight loss plateau by eating a Big Mac.