How is it more useful than the Big 5? I find the Big 5 to have far more explanatory power. Openness to Experience especially is an under-discussed factor in human relationships.
The fact that the MBTI frantically added a fifth type for neuroticism is all the evidence you that at best it's playing catch up real personality science. The MBTI is all about profiting off of a human desire for belonging, which is why all the examples that the major sites give for each type are historical heroes (are you more of an Abraham Lincoln or Joan of Arc). Neuroticism is a harder sell, but guess what? Thinking of myself as a sensitive/neurotic person has been extremely enlightening, more than all the MBTI results in the world.
I'm preaching to the choir, but I get fired up about this stuff.