It’s like any other initial screening tool. It gets you started, but it can’t be the main determinant for healthcare. BMI isn’t meant to be an all-in-one measuring stick the way something like a blood test can be (most of them are first steps as well, but there’s exceptions).

If a doctor has a patient with a 30 BMI, but they can see that you’re at an otherwise healthy body fat level, they won’t try and treat you based on the BMI unless they’re on the shitty end of doctoring. There are bad doctors, but most of them get weeded out in the grinder that is med school and internship.

You’d definitely want to have other measurements to go along with BMI when you’re unusually tall, short, or muscular.