Hey Ruckus, that article went on about how having a bodyfat percentage that your body was comfortable with(not too low) is muscle sparing. When it needs more energy, like when you're sleeping, it can dig in to bodyfat stores rather than catabolizing muscle. The lower bodyfat you have, the more likely your body is to use muscle as a fuel source.
As for the main question..
When you pass a certain point, the bodyfat you carry has an estrogenic effect on the body, and it works the other way too. The estrogen your body produces because of the bodyfat = more bodyfat.
When you get down to a % that your frame is uncomfortable with(ie. you have to fight to maintain such a low bodyfat level), your test. levels start to drop and/because your thyroid starts to screw itself up.
dietary fats and bodyfat help regulate thyroid function/hormone levels(test., est./androgen), so being at a very low % can muck up your test. levels, as can being too high.
For most people 10-12% is ideal. The skinny guys do fine at 6-8% and the bigger guys can do well at 13-17%.
so it really depends on what your body is comfortable with. Different people react in different ways to various bodyfat levels, but a good middle-of-the-road place is 10-15% for 'bulking' and 'cutting'.