The drag is almost certainly a more minor consideration. They will have better effect in a propwash slipstream and that is a consideration.
However, I believe the major reason for their adoption is not Stability & control, but simply geometry and a/c arrangement. the rear fuselage can be of a different layout, without the internal fin structure encroaching.. i.e. space can be utilised further aft.
They were used in several WWII British engined bomber designs, to allow a rear turrent and access.