My dx of schizoaffective bipolar type ultimately led to the type of meds/ treatment that helped me the most however I do think that there's a spectrum with mental illness and there can be a lot of overlapping symptoms. The main thing that changed when my dx changed from bipolar to sza bipolar was that instead of just moodstabilizers and low to mid dose APs I got on a really strong high dose AP along with the moodstabilizers, which targets the psychotic symptoms that tend to be more constant in psychotic based disorders.

Anyway, many types of meds are used for multiple purposes, so I while I think having a correct diagnosis is very helpful and important, I don't think it's as big of a problem if you were to say be dx with something entirely different than schozophrenia or bipolar spectrum disorders like diagnosing someone with something blatantly wrong or not even close to the mark