Leader has two hands on follower, but less margin for error. More strength required of the follower. More strength and coodination required of the leader. Average worst-case scenario isn't so mild. Abortable up to a point.
Leader has one or no hands on follower after lift-off.
Follower assumes sole responsibility for landing safely. Narrower margin for error. Responsible for most professional dancer injuries. Ditto on the third person spotter. Average worst-case scenario includes broken bones.