fadecdegraded, I agree about not doing it in a 206 (pulling collective after shutdown to slow the blades), or at least being very cautious about it, as the transmission mounts (spring and cup type) can really get some nasty-sounding and feeling bounce going - I had to do it to stop the blades once when parked in a hillside pad with a very strong updraft, and it wasn't much fun.
The 205, on the other hand, with the 5-mount transmission, is a much better prospect, and I've certainly used collective many times to slow the blades after shutdown in those. I think the worst you can do in that case is make the blade grip reservoirs leak if you have them.
Comes down to the type you fly, naturally enough, and I certainly wouldn't rule it out as something never to be done if the need was there.