I clearly phrased this badly. I will be as precise as possible. Note that I've read about half of Why We Sleep, a year ago or so, before giving up because parts of it were such cult-like "I am going to write about how wonderful sleep is without actually paying any attention to the content of what I am writing"; I simply couldn't stand the nonsense evo-psych "explanations" every couple of pages. I'm aware that you don't get to be one of the top sleep scientists in the world without being capable of competent thought, but that book did not provide evidence of this fact. I also strongly believe that playing around with the amount of sleep you get each night is one of the highest-value experiments it's possible to do, because the cost of sleep is so enormously high and because its benefits are so high up to a point (and the graph of benefit against time varies from person to person).

The comment to which I replied, in part: "Do any of these errors reverse that information? Is sleep actually harmful?… If not, then what's the point [of arguing about whether Why We Sleep contains errors]?"

I interpret this comment as: "Why We Sleep may contain errors, but I don't care; sleep is obviously good for you. I know how much sleep is necessary for me, and am capable of ignoring whatever Why We Sleep says on the matter of how much is required."

My response is that we should care that Why We Sleep contains errors. People are going to read that book and use it to determine how much sleep they need, whether or not the parent commenter has done. The fact that Why We Sleep contains errors obviously doesn't mean we should get less sleep - the greatest idiot on Earth may say that it's raining, but that doesn't mean it's sunny outside - but it should make you at least a little sceptical of its arguments that you should get more sleep, because that sleep comes at a massive cost.

Suppose for the sake of argument it is the case that I require seven hours of sleep a night, and the additional eighth hour confers little additional benefit (or even confers harm - it doesn't matter to my argument). Suppose I habitually sleep seven hours, but then I read Why We Sleep and am terrified into sleeping eight hours a night. Now I am spending a full 1/24th of my life - about 4.1% of it - on extra sleep that is doing very little for me except robbing me of consciousness.

Perhaps it is the case that for you in particular, there is enough benefit from that eighth hour of sleep to outweigh the cost (and I assert that it's definitely worth everyone individually doing this little experiment on themselves, because people differ)! Perhaps it is the case that for most people, there is enough benefit - but we don't know, and we can't know simply from Why We Sleep, because it contains errors.

(The first part of the comment to which I replied was "The general message and key takeaway I got from the book was that sleep affects your health in various ways and getting a sufficient amount of higher quality sleep is better than not doing so." This is undoubtedly true: so obviously true, in fact, that there is no need for anyone to read a book to learn it.)