I'm really no expert but it does sound like the rider you're talking about simply was trying to avoid having to pull at the front, probably because he didn't have enough gas in the tank anymore or wanted some more rest before going into the wind again. I don't know if they talk about such specifics beforehand or it just develops during the stage but I think there's some value in carrying another rider like that along even if he can't stay at the front for a long period anymore, assuming he isn't slowing down the train.