The benefit has to do with the individual's autonomy. By living in an apartment, they learn not to depend on others and to take care of themselves. Rehabilitation begins with having self-esteem, your own things and feeling responsible. When they live in an institution, they have no decisions to make and have no responsibilities. So it becomes difficult to make them fully self-sufficient.
I went through that with my son. Over a seven-year period when everything was going well thanks to medication, he owned a three-apartment building. He took good care of it and functioned quite normally. For people like him, it is really important to have that feeling of belonging and accountability to be able to continue their rehabilitation in the community.