I know people who have had issues after assigning a specific channel (ie. the range dropped or the triggering was inconsistent for whatever reason).
Once the 600's become more popular, I may need to explicitly assign channels and ID's to avoid triggering other 600's that are in range....but so far this had not been a problem.
I did assign a channel once (I used channel 3 to test) and everything worked fine. I have 5 of these flashes so set everything back to auto on all flashes as I didn't want to have any that weren't on the channel I was expecting.
. You just can't win! 
