From personal observation I think it gives me some good hints. It's not even close to being the only factor but I find it useful.
Now, indeed nobody is a pure ESFJ nor a pure INTJ. People tend to get hung up a little bit too much on the letters.
[1] https://en.wikipedia.org/wiki/Jungian_cognitive_functions#Ex... [2] https://en.wikipedia.org/wiki/Jungian_cognitive_functions#Ex...