I know that it is a mode to prevent undesired thrust adjustments by possibly faulty autothrottle signals,...
Not only that but arguably more importantly,
Clamp allows tha pilot to close the throttles (should be thrust levers but MD/Boeing calls them throttles) if a rejected takeoff is desired/required, or, on a flex takeoff, max takeoff thrust is still available simply by pushing the throttles forward. If Autothrottle was still engaged, it would fight these manual thrust selections.