Here's a quote from the man himself, David Bynon, which explains his philosophy on the use of 3M SMR:
<blockquote class='ipsBlockquote' >
3M Perfect-It Rubbing Compound and Swirl Mark Remover are abrasives. They should only be used if you have micro-marring, not as a general purpose paint cleaner. If your paint is new, or otherwise perfect, use a show car polish to improve the finish, not an abrasive compound or polish.
With that warning out of the way, let it be known that I am one of those people who does frequently polish their paint (2-3 times a year). I do so because polishing with a good polish helps to level the paint surface, which in turn makes the paint finish look better.</blockquote>
If you're interested, the article in its entirety can be found
here.
Personally, I believe that you'd have to use a whole hell of a lot of 3M SMR to cause any significant damage to your clearcoat. It's a very, very mild abrasive -- I've had to use three to four applications (with a PC, no less) of it in some spots to remove some minor swirl marks which were present when I took delivery of my car. Of course, don't use it if you're not trying to fix micromarring -- but I really think a once-a-year application would be fine.
How much clearcoat you "remove" also depends on how much SMR you apply and what type of polishing pad/method you use. I use a very, very small amount of SMR (about the size of a dime for an area about 1/4 to 1/3 the size of the hood) when I polish out any swirl marks, and I only use a white polishing pad with my PC, never anything harsher.
Of course, I may eat my words in ten years when I don't have any clearcoat left!
