Au contraire - he's going to need to buy RER tickets in any case, so why not buy the zones 1-2 Navigo at the same time and avoid standing in line twice?
True -- I was thinking about getting the photo (do they have a photomaton at CDG/Roissypole?) and assembling the pass. But indeed better not to stand in line more than necessary. I personally would prefer not to have my mug shot taken when I'm fresh off the redeye but that's a separate step.