I've been camped out around 12% for a while and through experimentation have found what choices make me a little leaner or a little less lean, so I'm confident I could camp out at 10% or so, but that decision would be based on narcissism, not health. Over the years, I have heard and read many times accounts of people who claim to get sick far more often at a low bodyfat %. Vitamins A, D, E and K are stored primarily in fat, but I wonder if a consistently high intake of these via strongly nutritious foods that are not subject to seasonality might make our fat-soluble vitamin buffer unnecessary. Clearly, adipose tissue has endocrine and other functions, but these would not really be negatively effected by a sparse amount of fat stored in these cells.
Perusing pictures of many types of contemporary hunter gatherers shows a variable but narrow range that is likely 10-15% for males and 20-25% for females on average, but that doesn't really tells us what is optimal for health and longevity, just that higher amounts of fat don't "naturally" occur.
If we subscribe to Taubes' theories, then a correct dietary carbohydrate content will result in an ideal bodyfat %, regardless of how many calories we take in or how much exercise we do. I'm still not wholly convinced that this occurs, and even if it were true, it would be difficult to figure out which level of carbohydrates is optimal. He seems to argue that each level of carbohydrate intake (accounting for type, and outside of starvation) has a corresponding hormonal response which assigns people to a particular body composition. The high variability among past and present hunter gatherers with regard to carb intake coupled with the low variability in apparent BF% makes this unhelpful for the task at hand.
Have you fellows any anecdotes or thoughts to share on the subject?