Originally Posted by HalfSlant
BMI is used by health professionals, but mainly only when talking about morbidly obese people. For example when a Dr says they have a patient with a BMI of 40 vs one with BMI 50, the nurses or whatever know exactly what they mean. Easier than saying.. I have a patient who is fat as ****, but not fatter than ****.
It's also used because getting a meaningful measurement is difficult, so this is something that anyone can figure out very easily (pretty much everyone knows their height and weight), and can "classify" you at least somewhere. Most people are extremely lazy when it comes to health related issues, and if you need something extremely basic requiring the minimal amount of information with no special equipment, that's about as good as its going to come. Anyone who is the exception to the rule (typically people who actually have muscle mass), they aren't going to be as lazy and know it is garbage, and be able to jump through a few more hoops to come up with something meaningful.