It measures what it measures (a bit like the IQ test). The same person can give different responses at different times depending on a number of factors, resulting in different measurements over time.

There are other and more useful measures, such as the Big Five as mentioned by @Matias

I found this interesting talk on personality types:

They compared MBTI types to neuroscans by EEG. It says they are identifiable.

I've heard it called 'astrology for those that don't believe in astrology.'

Here are some links I pulled together early in 2018 when I was curious about such personality tests.

[shrm.org]
[vox.com]
[theguardian.com]
[skeptoid.com]

It was developed by people with no formal psychology training and has very poor test-retest reliability. Every time you take the real one (not some little 20 question stuff you find on the web), you are likely to have a different type... It isn't scientific or valid, and has no predictive ability.

I took it for the 1st time today and found I was an EST J. It was frustrating to me that Up this I had to pick because each time I felt I had characteristics from both sides.

Since the actual question was whether or not I believe in it, I will have to say I think it is moderately correct.

I found it to be illuminating. It helped me focus on personality characteristics as being akin to right handedness or left handedness. The idea that personality characteristics may not be a choice.

I think it's a parlor game. It was invented by a mother-daughter duo as a way to see personalities. However, it has failed every scientific attempt at validation, and should just be used for entertainment.

I’ve found it useful in self examination, as did my now adult children, as several college classes suggested they take it. A stepping stone to a broad set of personality possibilities, often in need of refining on a personal level..

Thinking not needed, as far as I know scientists long ago abandoned it as being sketchy science at best. It's basically pop psychology now, little better than astrology the way people use it.

I don’t know how scientific it is...but it seems reasonably to have summed up my personality type....when I took the test it assessed me as ESFP...which according to them makes up only 5% of the population.