It's basically for plinking when .22 gets boringI have a 9mm / .357 convertible and I often use both cylinders. I've never considered its use with 9mm to be anything besides a convenience / emergency / way-to-use-less-expensive-ammo feature because of the mismatch of .355" bullets in a .357" bore. Certainly jacketed bullets can sometimes perform fairly well in the case of a slightly undersize bullet, but no matter what it is sub-optimum.
Also we need to keep in mind that 9mm Range Ammo, factory reloads and steel case were dirt cheap when Ruger started offering the 357/9mm convertibles so people probably weren't as worried about mediocre accuracy to pop coffee cans or pie plates with 9mm you could get almost as cheap as .22
It's only in these recent years that I honestly really even worried about the group spread. When Tulammo 9mm was 90 bucks per case I popped 1000s of rounds of that stuff through these Blackhawks just hanging out at the gun club for an afternoon , along with some autochuckers