Ehh... there's a lot of issues with the tests, and that's the main thing I was calling out, but I still don't think it's a particularly great or useful theory. As you say, it isn't really falsifiable, so it's pseudo-science at best. But let's put that aside and speak purely about practicality.
I just don't see how finding a predetermined type that you feel defines you better than the other predetermined types among a set of an arbitrary number of predetermined types is a very good way of helping an individual better understand themselves.
Some people, when they discover which category they fall in (probably from taking one of the tests) think along the lines of "now I understand
why I'm the way I am!" but that's a horrible way of interpreting the intent of the theory, since it assumes that there's some actually present type (like, physically in the world, a particular way certain brains work) that you fall into that determines how you think and act. Nothing against the theory explicitly, but that's a potentially dangerous mistaken assumption to make.
Another problem that isn't explicitly the theory's fault is that, despite it not being recommended or probably even legal to do so, I've heard tell of some employers actually utilizing MBTI in important decisions (hiring/firing/promoting/who-works-with-who/etc.), and that
is a pretty awful thing.
Basically, the theory alone is fine and harmless, but it gets misused and misunderstood in so many ways that, since it isn't very valuable in itself in my opinion, I'd rather it just kind of be forgotten and put aside, tbh.
Really, though, I was just poking some fun and pointing out some statistics because I find the tests silly and unreliable, but you forced me to think about it a bit more deeply, and this is what I came up with.
EDIT: Haha, I feel like I'm making a weird first(ish) impression here. I've lurked occasionally, but this is really the only stuff I get worked up enough about to bother to actually post.