Mass dampers are to help quell or reduce vibrations, so I would imagine that this application is to help eliminate/reduce chatter under deceleration and possibly even help with grip under acceleration. It helps pick up where the compressing/rebound damping in the rear shock itself may fall short. Pretty sure when Ducati came out with their "salad box" rear subframe many thought it contained some sort of mass damper or gyroscope, until it was revealed it was just to relocate electronics to allow for more varied front-end aerodynamic designs.
I remember reading that about the Ducati, and there was mention of a rider (Schwantz?) during the 500 days who would haul ass in practice and qualifying but the bike would behave differently in the race. It turned out the data logging equipment they removed before each race was helping by keeping the bike stable during practice, and changed the dynamics of the bike during the race because they took the weight away.
Redding saga continues... https://www.crash.net/motogp/news/903440/1/redding-apologises-aprilia-postaustrian-race-comments
Sounds like someone realized that he should quiet down and keep collecting a check for the rest of the year.