The tests are wildly inaccurate, and MBTI itself is not the full story of cognition and personality, but I think there is enough evidence suggesting that the cognitive functions as described by Jung[0] are very real.

The article you linked to uses lack of MBTI in psychology journals as an argument against its validity, but its applications in the field are very limited. You're more likely to find MBTI references in neuroscience journals as there are appears to be clear correlations between type preferences and brain activity patterns[1].

Even so, knowledge of a persons cognitive preferences just isn't very useful. So the main application of MBTI is indeed "just for fun".

0: http://psychclassics.yorku.ca/Jung/types.htm

1: https://www.youtube.com/watch?v=MGfhQTbcqmA

it's pretty useful for those who have a difficult time understanding and getting along with people otherwise.

The way I would use this test: See each dualism as a continuous dimension. Reflect where I probably fall on each dimension at this time. Think and point out where I would like to fall. Personally I'd prefer to fall on the middle of each dualism. This gives me some hints what in my personality needs to change first if I greedyly want to optimize.