Todd@RUPES
Just a regular guy
Its interesting that there are still well known detailers on the major detailing boards who suggest you can use M105 all the time without checking paint levels. And here you are, a proven high end detailer, suggesting to be careful with M205... Its incredible that there can still be this big a gap in terms of care...
While I wouldn't advocate using M105 all of the time (in a reckless manner) products like M105 and M205 are only as aggressive as the user. M105, by function of the abrasives used, is more like a finishing polish that has the ability to be very aggressive vs. an aggressive compound that finishes nice.
I am sure that a great many professional detailers (particularly those who are experienced with M105) have a good feel of what they are doing and may not find it necessary to monitor paint levels (based on their experience). But being a professional with 100s (1000s) of cars under your belt is a far different situation than an avid enthusiast who just wants their car to look great because they love their car (and does not want to damage it for the same reason).
Because of the huge experience gap it is often necessary for enthusiasts to be far more careful, even when using a far less aggressive technique.