As an example: some situations call for being very detail oriented (J), where some situations call for being big picture (P). If you know you are prone to one or the other, you can either let others handle those situations, or realize that you are outside your comfort zone and be extra intentional.
The issue is you might do the test today without a morning coffe and 5 years from now after a good night sleep and get a large results disparity.
So either we accept that we as people keep changing the personality, that this tests for, thus making the test meaningless. Or we accept that inter test reliability is not great, which also makes the test meaningless.
Most of the people using these models in practice aren't claiming that you can find your type after just taking a test. Most who are being honest about it (instead of trying to make a quick buck) will warn you that it can take years of introspection to figure out what are the biases that consistently lead you to shoot yourself in the foot in life.
Eg, have a look at some of the early stuff by Objective Personality (not the last year or two when they started getting more commercial.) Constant warnings about people mistyping themselves and the need to consider feedback from a wide variety of people and situations before making any conclusions about yourself.
I remember taking this test many moons ago as an intern, it was never said explicitly but it was clear later on that the test was used by HR and multiple engineering teams to advise who would be put on a management track of that batch of new employees.