As suspension, particularly when a car is used on the roads (where you are not measuring performance in 1/10ths of a second) is subjective and individuals preferences vary significantly, surely the biggest benefit is that adjustable dampers can be tailored for / by the individual to suit their driving style / the roads they use. My old 410 Exige came from Lotus on 3 way Nitrons, on the roads I drove it was too stiff (for the speeds that I was driving) a couple of clicks adjustment and the car flowed, whether this meant the car was quicker is purely academic on the road, but it was a much more pleasant ride, and the car seemed to work with the road rather than against it. Similar situation with Core dampers that Meteor fitted to my CSR, too stiff for my taste, but being able to back off the damping meant they were pretty much perfect (for me). Compare this to the Aero 8 that I had, on non adjustable dampers, which would quite literally get airborne when driven down a bumpy road at speed, if some adjustment has been available it would very likely still be in the garage. If you look at motorcycles, non adjustable damping is seen as a budget option, and the first thing you would do with a new bike is set the suspension for your weight and riding style.