Suspension bushes are amongst the most stressed parts fitted to any Bentley. They not only have to cope with every vehicle bump and vibration they have to deal with engine heat, contamination on the road/from the vehicle and a lack of lubrication. With age rubber bushes breakdown, they may become dry and cracked and lose their noise/vibration absorbing properties, they often introduce unwanted flex into chassis system. 
Powerflex bushes do not deteriorate with age and are impervious to heat and contamination. You can fit and forget them because they won't wear out.