Mart,
Preamble: It is assumed that we are talking about a
servo-flap and not a
servo mechanism
Trivia: Kaman's first full-scale rotor. Note the leading
and trailing tabs.
The servo-flap (elevator trimmer) on an airplane is used to adjust for the location of the craft's center of gravity. It is used to eliminate any longitudinal force on the pilot's control 'stick'. It is normally only adjusted when the pilot changes the craft's attitude, such as climb, cruise, slow descent.
You are probably correct in that the servo-flap control of a helicopter may reduce perturbation induced vibrations; in the craft and in the cyclic stick.
The question in my previous posting relates to the relatively slow response time of helicopters. IMO, the servo-flap control adds an addition function (delay) in the chain of activities between the pilot's action and the aerodynamic response of the rotor.
Dave