where I live, injections are mostly used with "court orders." Basically, if a patient is committed to a state funded facility, upon release a judge rubber stamps an order for 6 or 12 moths of forced treatment. I don't know what happens if the person doesn't show up for their injection, but...nothing good, clearly.

the other situation in which injections are used (again, where I live, at the clinic I go to) is to get around insurance weirdness. So, if a patient needs 2 tranquilizers, one can be administered via injection and another can be prescribed and filled at a pharmacy.

Personally...I would not want to do a long acting injection. Once injected, you're stuck with it for a while (I think most shots last 1 month; there's a Invega one that lasts 3 months), and there's not much one can do if serious adverse effects pop up.