It's helpful towards understanding yourself You're right in that your MBTI type is not really your personality and you should not mold yourself to fit the archetype of the type you identify yourself as, but it's still excellent for self-awareness and understanding how other people see you. For example if you test/identify as an INTP and read about the cognitive functions of an INTP along with archetypes, and you realize what it is those cognitive functions do, you become more metacognitive and understand how the framework of your thought process differs from other people, so you have a more objective understanding of yourself. It's also great for knowing where your weaknesses and gaps are because you can now compare yourself to other INTPs. I know you shouldn't change yourself just because you want to fit more into the box of your type, but sometimes it might be something to take into consideration. If your first two functions are geared towards depersonalizing and abstracting the shit out of everything, and you find yourself struggling at tasks that utilize such qualities, then maybe you need to reevaluate your life priorities.

It's helpful in understanding other people and other thought processes It's great towards understanding other people and ways of looking at things. MBTI isn't really a science, but it's still helpful because you cannot deny that other people simply think differently. If I have a teacher who keeps returning essays to me that says I need to be more expressive about my opinions, or I'm opinionated enough in general, maybe I can assume they make judgements through Fi and I can try to put myself in their shoes and fake it, or at least realize that we just aren't on the same page. A lot of concepts and activities utilize certain functions. Since I know about Ni, I now know that there are people who can seemingly foresee events, which explains many achievements made in prophetic and scientific phenomena, and that maybe this is a way of thinking I need to take less for granted. It helps you realize certain people's thought processes are just fundamentally different from those of others, and of their importance.