According to Historic England, “Listing is the term given to the practice of listing buildings, scheduling monuments, registering parks, gardens and battlefields, and protecting wreck sites.”
It means the hospital CANNOT be demolished to make way for another housing estate. Both buildings could, theoretically, be converted to flats, but they’re huge buildings. Developers may struggle to fill them with enough buyers to make a return on their investment. I can’t imagine other uses for the buildings, given where they are and their sheer size.