But doesn't the sub-sonic ammo have less energy and different impact point than regular ammo? So wouldn't it be for just plinking anyway?
It all depends. To give you an example.
I have a 300blackout SBR that I shoot suppressed with subsonic ammo (220gr).
I shot it unsuppressed with subsonic ammo and zeroed the EoTech with the rifle.
I then added the suppressor, shot several groups, and then noted where the zero needed to be and adjusted. (about an inch)
Now it's zeroed suppressed out to 100yds and I have drop information out to 200yds.
It's a dedicated subsonic gun now.
With a pistol, like say a 9mm, the difference between 115gr (super) and 147gr (sub) is negligible at the distances that I would have the expectation of using that gun.
As with everything, your mileage may vary.