The reason I had two bags was that I did not expect to be joining that line and was unable to leave it elsewhere, someone might nick it
Also having two bags is also good for the training as the dog may have no problem in getting a wiff but then might want to give up when he/she doesnt get the right bag and therefore doesnt indicate to the handler. The handler would not really notice how many bags you have he/she is watching the dog and its reactions.
In fact agree with both areas of the replies. I can understand why he did it but why did it take so long for the message to get to him?