VERY helpful in figuring out how many calories you "need" a day to survive-- and from there you can figure out how many you want to have.
No wonder I always gained weight so easily on the "normal" 2000 a day. My BMR is 1445.
IMPORTANT NOTE: That number is just what your body burns normally, at rest, on its own. If you exercise or even just move around during the day, it'll burn more.