Well, both. Personally, I use 3M's SMR for dark when I really want to get *rid* of them.
For example, when I first got the car (it's about a month old now), there were some swirls on the passenger's side rear quarter (from dealer, as this was going to be my first wash). So, what I did was spot SMR them in the garage w/ PC. Taking it back into the sun, I noticed that some were gone, and some reduced. I didn't bother to do it again to get it completely perfect.
It WILL actually get rid of them. All you have to do is use a 50/50 mix of water / IPA (rubbing alcohol) to remove fillers and see what's there. Or, if you're using a paint cleaner after SMR, that'll do it, as well.