It looks (to someone who has not done any of the necessary research to draw any real, useful conclusions) that they are proposing a balance of sorts. You are sa

It looks (to someone who has not done any of the necessary research to draw any real, useful conclusions) that they are proposing a balance of sorts. You are safest (in this theory) when sleeping. You are likely holed up some where, hidden from view, and relatively non-moving because you are unconscious. To cope with the inherent danger of being unconscious, you are especially alert to particular sounds which may signal a coming attack. While awake, you are out, moving around, and under danger of being attacked by a predator. However, there must be a balance between the two, because there are certain things you must do to keep living (find food, eat, create shelter for the next sleep period). Its seems fairly reasonable that there is a balance point in there some place, and that it would be different based on each animal, depending on the habits of not only their prey and predators, but also how much food they must bring into their body, what kind of shelter their environment requires for sleep, and all sort of other factors.