I don't know how many facilities are providing this sort of centralized treatment, but I have doubts about how effective this is if it is not personalized to the specific needs of individual patients. The question as to what works best for mental disorders can't be answered generically. For example, acutely psychotic schizophrenic patients have vastly different needs than stable, personality-disordered patients experiencing adjustment disorders.
Substance abusers have different needs than demented patients.
There is no one size fits all approach to treatment when it comes to mental illness. The type of treatment is more important, I believe, than whether it is provided in one central facility or not. One problem with day treatment programs for psychiatric inpatients is that they may be overly stimulating for some acutely ill patients, but too basic for less severely disturbed patients. For example, group therapy that is overly-intrusive or uncovering can actually make some schizophrenic patients worse.