It is quite important to be aero when leading, or otherwise when isolated in a descent, in order to gain speed while being able to rest. Others that are riding

It is quite important to be aero when leading, or otherwise when isolated in a descent, in order to gain speed while being able to rest. Others that are riding in a group may have a sub-optimal position in a descent and pedal to compensate. They will be able to rest on the flat anyway by relaying each others at the front.