In the 2011 fatal accident, the elevator trim tabs began fluttering due to wear on part of the linkage. With the loss of an effective trim system, the aircraft abruptly pitched up with as much force as 17 Gs, which caused the pilot to black out. (After the pitch up, the trim tab separated from the left elevator.) (airspacemag)

When you move the trim tab up or down, it sticks out into the free air stream, and deflects the elevator in the opposite direction. So even though it may seem 'backwards' to move the tab down to make the nose of the plane go up, seeing the tab in action helps it all make sense. (Boldmethod)

Another advantage of using trim tabs is that they protect the airplane from premature wear and tear. If an airplane doesn’t have trim tabs, it will be exposed to greater stress and pressure during flight. Over time, constant exposure to this stress and pressure may cause some of the airplane’s components to fail early. (Monroe Aerospace)