I guess my regular spot-claying is a different approach than many employ...my wash regimen is so gentle that it doesn't always get *all* the conatmination off the vehicle. I use the Sonus green (very, very carefully) to remove what's still there instead of washing more aggressively.
As long as I'm careful (i.e., one short, light stroke, inspect clay for contamination, knead, replace clay after about three of those) I don't have any problems. Gotta watch that you don't move the clay across the paint once it's picked up contamination.
Yeah, I go through a *lot* of little pieces of clay. It's just my way of doing things, to me clay is a renewable resource and an easy way to clean things up without marring or even comromising my LSP.
But as RAG and I are noting, this sort of claying is completely different from doing the entire car. I don't clay the whole thing unless I'm redoing the LSP or preparing to otherwise do a full detail. When claying before redoing the LSP you have to be very careful not to mar...the clay might pick up contamination that you didn't notice was there; it's not the *clay* that does the marring (if you use the right clay properly), but rather something abrasive that gets *stuck* to the clay.