I think he's probably a rider who put in a lot of effort early and isn't able to contribute. Saw with one team the guy on the back was reaching forward and guiding in the rider dropping back with his hand.

The minimum number of riders in a team to cross the line is 5 so even a spent rider could be crucial if there was a problem that reduced the number to 4. The time is calculated on the 5th rider to cross the line. HTC had only 5 riders when they crossed the line which was living dangerously.