The shroud is there as an 'anti-spin' device. It serves a few functions as it has been explained by the engineers in Italy.
a) RPM and safety concerns - certainly none of us are free spinning our machines in open air, but reducing the RPM of the plate is a safety feature to prevent foams and plates (which do have a threshold for safe RPM tolerance) from catastrophic failure. Certainly no one is going to be killed by foam pad shrapnel, but the regulations exist that require foams to be RPM rated and the devices on which they are used to prevent rotation in excess of that rating.
b) Preventing excessive rotation - the tools, pads, compounds are designed to work as a system and that system is designed with a pretty specific RPM range in mind for maximum performance. We can all argue that more rotation equates to better correction to a point, but there is a point where excessive rotation can become detrimental to the process as well as increase the 'risk' factor to the operator creating an undesired result (overheating a pad, cooking the compound, burning an edge however unlikely) so the shroud works like a safety brake to slow rotation to the levels the engineers found optimal with the system.
c) Compound sling - the pad is stopped quickly from free spinning once the machine is shut down, this prevents unwanted compound sling. Again... few of us are lifting the pad off the surface while its still rotating, but this does prevent that cast off issue.
With Mark II RUPES recognized that the market has caught up (skill wise) with large orbit tools. If anyone remembers back to when BigFoot first showed up a number of people struggled to grasp the concept and apply it correctly. Polishing like it was a PC 7424xp, pressing hard down, cooking pads and getting poor results. As the general competency of the operators has improved Mark II delivers the additional power to continue the rotational movement regardless of panel shape, thus somewhat defeating the need for shroud over-rides. I'd challenge anyone to show me improved performance on a 15 Mark II modded over the stock configuration.
Todd can elaborate more as well, but thats my info direct from the source as it has been explained to me and my personal observations with the tools (modded and unmodded)