Reversible flight controls in light airplanes are self-centering due to aerodynamic forces acting on the control surfaces. If properly set up and maintained, the friction will ensure they return to their trimmed condition.
Reversible controls in helicopters (R-22, Schweizer 300, MD500 series) are not necessarily self-centering due to loads fed back from the rotor blades. These forces vary with the flight condition and a host of other variables. But they are not the same as a reversible control fixed wing airplane.
Aircraft with irreversible flight controls (hydraulically boosted typically) have to employ artificial feel systems to try to duplicate the situation found in a reversible control system. Typically this involves a force gradient system, with a motor to trim (in fixed wing and some helicopters) and in nearly all helicopters with artificial feel, a trim release system.
Trim release is merely a faster acting way to reduce the control forces to zero at a specific stick position.