The human body saves a lot more energy than one frankfurter bun though sleep by simply not moving all that much [...] Bats, sleep 18-20 hours per day vs. giraffes which sleep 3-4 hours per day etc.
I see. I think what you are talking about is not even energy expenditure but what we call "the null hypothesis". Basically says that there might be no other active function than sleep other than resting as a mean to escape predators and not using energy. This is far from being the accepted hypothesis on sleep function: in fact there is basically only one guy who still talks about this (Jerome Siegel, UCLA); the rest of the community is pretty much convinced that this is not the case.
I'd suggest you reading this on the matter:
http://www.plosbiology.org/article/info:doi/10.1371/journal.... (it is open access).
I think we are talking past each other. I suspect sleep does a lot of useful things. Just as humans lost the ability to produce vitamin C we may have become dependent on sleep for things that are not required in theory. So there may be layers of dependence that show up over time. My suggestion is talking about what sleep does can be separated from the fact that sleep is so common and needed.
PS: Your liver does many things necessary for you to live. It also does many things that help you live a better life. Talking about what your liver or sleep does, without including the useful side effects is not the full story. Sleep deprivation hinders memory formation in humans and hinders reaction times. Are those related to the core function of sleep or just a codependence developed due to other useful features of sleep? I don’t think there is a clear separation between the two.
As an observer, I appreciate the debate, and I'll add that it doesn't seem to me like you're talking past each other. Giving the other gentlemen the benefit of the doubt that he's something of an expert on this subject, it seems he's very clearly understanding your point and offering his opinion to the contrary.
I, myself, have nothing much to add in the way of hard facts, but using logic, I think that sleep-as-an-energy-saver seems off. Sleep seems like a highly vulnerable state for early animals. If the only initial benefit of sleep was energy conservation, it seems like animals that simply chose to rest would have an edge upon those that slept. By resting, they'd conserve the same energy, but would stay alert and responsive.
And it interests me that animals that cannot rest (sharks, for example) still sleep.
I see. I think what you are talking about is not even energy expenditure but what we call "the null hypothesis". Basically says that there might be no other active function than sleep other than resting as a mean to escape predators and not using energy. This is far from being the accepted hypothesis on sleep function: in fact there is basically only one guy who still talks about this (Jerome Siegel, UCLA); the rest of the community is pretty much convinced that this is not the case. I'd suggest you reading this on the matter: http://www.plosbiology.org/article/info:doi/10.1371/journal.... (it is open access).