BMI is useful for screening and population studies, but it's (mostly) bullshit for individuals. For most people it's body composition that really matters. Excess adipose tissue, especially visceral fat, has a wide range of negative health effects. Anyone who cares about their health should get a DXA scan at least every few years; it will give a highly accurate reading on body composition including fat distribution.

When I was 16 I waffled between the top edge of healthy and the bottom edge of overweight, according to BMI. When I dropped into the top edge of healthy I had a 6-pack. I wasn't even that muscular, just broad-shouldered.

BMI is pretty good for populations.

If you are standing in front of your doctor and he or she is telling you that you are obese because of your BMI score and not actually measuring you (like with calipers), I’d probably look for a new doctor.

Calipers are not the proper medical standard of care for measuring body composition. They don't produce accurate, repeatable results. The current best practice for most patients is a DXA scan.

How many physicians can do a DXA scan in their office? Calipers give you ballpark numbers and often that's good enough for a physician. It's certainly better than BMI.