The pistol round can be more easily suppressed and easier to get reliability out of a short gun than any of the rifle rounds.
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Compared to, say, .45 ACP in a PCC it's downside is cost/availability. Upside is exemplary range and terminal performance with good supersonic ammo and the ability to reliably run both supersonic and subsonic in the same gun with no changes.
Works great in barrels at least as short as 8"