Ive read about Sheldon before, his work breaks down because he tied it to personality and character types, though the physical body typing he used has been adapted elsewhere as a loose description of genetic shape. No one person will likely have 100% of the characteristics but it's the dominanat characteristic that is used to make the determination. It is useful in the sense that science has had a tough time describing genetic differences and predispositions, add to this that it's a touchy subject for most people with a spotty history of genetic views people have held over the years. Ultimately, though body typing is a good guide, it's not something to adhere to 100%, and results are more important than typing.
There are also attempts to make other body typing classifications systems, but so far none have become widely used.
Edit: It is "scientific" in the sense that there was an effort to quantify these physical body types in a complex formula, and this is the information that is still useful, even if the psychological pseudoscience isn't. The likelihood anyone is put through such classification these days when they are assessed is unlikely, but a general survey can be made.