Personally, I used to be pretty underweight (BMI 17 as a male) and had to gain 10 kg to get to "normal weight". I made it and it has made a huge difference on my ability to absorb training. So I guess the general idea can be helpful on an individual level.
That being said, statistically I believe that a BMI of 27 is often better than, say, a 23. So as long as your general health is good and you feel good you probably should not stress about it. And as others have mentioned, it does not account for your body composition. Which kind of fat (brown, white), how much muscle mass, etc. and it does not account for blood markers.