There's two things.
Control speed. While the output is the same, the automatic control is much faster than the human control. Especially on the rudder, CT can reduce drag beyond what the human being can do. A rudder-only CT would be a real advantage.
Real trim tabs. Trimming in the same direction as stick input does not increase the output. On the contrary, depending on how the trimming works in the plane. Normal trim tabs extend at the end of the control surface, and move in the opposite direction. Trimming nose up makes the trim tab go down, which in turn makes the control surface go up (pushing the tail down, and the nose up). As a consequence, trimming into the desired output reduces the effective size of the control surface. Making it easier to move, but also reducing the effective output at maximum deflection.
(anecdotal evidence: At least one real POH advises against trimming nose down for inverted maneuvers to retain the maximum effect.)