If the leader has had to resort to pulling on a piece of gear to make it through a crux on a pitch how can the second pass this point while also cleaning the piece that was used for aid. Assuming they are not a stronger climber than the leader.
quick glossary. "french free" and A0 are the same thing, both referring to pulling on a piece of climbing equipment attached to the rock when a climber is unable to pass a difficulty. Cleaning is removing equipment that the first climber has placed to prevent themselves falling to the ground in case of a fall. A crux is just the hardest part of a climb, it could take many physical forms. hope that helps. If not here is a more extensive glossary