There is pretty clear evidence that some subset of schizophrenic diagnosis are due to autoimmune issues. If we can use antibodies in the spinal fluid to detect when autoimmune treatments can be effective in treating schizophrenia, that alone will be huge.
However, the even bigger insight to be drawn from all of this is the potential for other psychological problems that psychiatry has struggled to treat, to also have autoimmune causes. When you try to treat something that has multiple, quite different causes, with a single treatment, it makes sense that it would be hard to find that treatment that works reliably (as is the case for many psychiatric medicines.)
I predict we may eventually see immune antibody tests (or some functional successor) become a standard part of all mental health care.