Using type theory and using assessments are two different things. Most type assessments only work on normal people and were designed that way, so you aren't going to get accurate results from any instrument.
On the other hand, Jung used type clinically. That's where it came from --different pathways for therapy got different types unstuck.
A realtime, effective use of type. A colleague of mine in Canada runs a preschool for children of autism. While any type can be autistic, she thinks about it as an exaggerated form of ISTJ--inability to relate to the external world, obsessions on physical objects, inability to put oneself into the shoes of others, and lack of openness. Note that this is total lack of ENFP, which is not how ISTJ appears in normal people.
The parents she works with love this lens--it's easier for them to relate to since they can relate through the type framework better than through "Your child is broken.."
With wonderful results, the preschool uses techniques and structures that Quenk and others found effective in reducing stress in ISTJs.
A bit scary that that's my type, but wow.
This is good for myself so that if I see myself falling into these extreme negative patterns, I can do something about it.