The MBTI is intended to measure your inborn preferences, and no more than that. Understanding your preferences can help you in all sorts of ways, a few examples of which are given here. The concept of preference is different from the concept of competence. Sometimes you are more competent in things that you prefer (e.g.: in writing with your preferred hand). However, you can - and do - develop competence in your non-preferences.

Bad Joke: Dr Watson's lack of competence in thinking was illustrated when he and Sherlock Holmes were camping. In the middle of the night, Holmes asked Watson what he could see. "Stars" said Watson. "And what does that tell you?" asked Holmes. "That we are small beings in the magnificence of the universe" replied Watson. "You oaf..." replied Holmes "...it should tell you that someone has stolen our tent!"