I don't know who Caner is, but here is you answer courtesy of the tour:
> Hello Caner ! Great question ! It is indeed always important for a leader to have at least one teammate alongside him on climbs, even though the drafting effect is less pronounced than on the flat, it certainly exists, especially at speeds above 20 km/h like on the Col d’Aspin. Furthermore, beyond the psychological boost of being surrounded by teammates, they can assist their leader in the event of a mechanical issue, shield him from the wind, and keep him positioned at the front of the peloton.