I personally like doing long distances fixed because I enjoy pushing my body to the limit and not relying on shifting or coasting to make it easier. For all the BS about 'zen', riding fixed for hours and hours brings me a hell of a lot closer to the 'bike and rider as one' stuff that so many people talk about. You bomb hills as hard as you can so you can make it up as much of the next incline as possible without having to tap into your dwindling energy reserves. Your muscles ache, your lungs burn, and you feel like you're going to pass out. When you get home, laying down and not spinning feels like the greatest time of your life. And when next you go out on geared bike, it feels like it's powering itself.
Sure it's less efficient, but if you're riding to push yourself hard and get a brutal workout, it's it own reward. Gears are a lot better in most ways but not all.