As a tool that seems to be primarily marketed for use by professionals and knowledgeable DIYers, why has Rupes decided to include such a thing as an "anti-spin" feature? There seems to be no benefit that I can think of other than protecting an inexperienced user from slinging product by lifting the pad while at full throttle.
A few points to consider...
While many of the professional market online (whether it be forums or facebook/social media) are truly high-end guys with some base of knowledge, the overwhelming majority of professionals are not quite as educated as this sampling would lead you to believe.
There are (depending on whose numbers you believe) between 95,000 and 165,000 body shops in the USA alone, each with an average of 3 painters and half with a "painter's helper". That means there are 300,000-400,000 people in the US who buff paint at this level.
There is also 10,000-20,000 detail centers in the US, although it is very hard to determine how many actually buff paint. Add that to the rough estimate that probably less than 1 in 100 mobile detailers ever find their into these places of higher learning and we have a huge number of professionals with a huge gap in ability and knowledge.
So, from a numbers game and after spending over a year in the field, I think the Anti-Spin shroud is a great idea.
Secondly, and frankly more importantly, RUPES tools are made in South Europe where the safety regulations are extremely tight. It could be hypothesized that this is a direct result of socialized medicine...
In the US, if you hands go number or you lose hearing... hopefully you have saved enough money after retirement to get a hearing aid or have surgery. In Europe, any long-term damage to employees is the responsibility of the government. Therefore regulations on vibration, safety, decibels, etc is extremely high.
So the tools, as a matter of regulation but also as a matter of pride, have to be presented in a manner that is completely safe, quite, and vibration free.
The primary reason is for the Anti-Spin shroud is to prevent the pad from overspeeding in free air. If the 15 MKII is allowed to free spin, the pad speed can reach 5000 RPM. The foam structure of the pad can become compromised with this level of stress.
For educated prosumers and professionals, this isn't a problem. For a lot of professionals making a switch to random orbital polisher after using a rotary for 10 years, it can be.
The BigFoot pads and compounds are designed for use with the anti-spin shroud in place and any difference in performance is negligible. However, if you use smaller or different pads, different compounds, and move outside of the system, you may find better performance without it (particularly if you polish with the legacy tools on lower speeds).
Sorry for the long winded answer, but I hope this answers the question thoroughly?