Dani, I think you're confused.
This discussion is about safety pilots who are sitting on the jump seat when a new pilot is undergoing initial line training on a multi crew aircraft. The safety pilot will do the following:-
1) Supervise the new pilot to ensure that they do not miss anything, or do anything incorrectly.
2) Monitor the training captain, as the new pilot will be like a fish out of water and is unlikely to pick up or question any mistakes that the trainer could make.
3) Take care of the paperwork to reduce the workload of the new pilot.
I would say they are essential during the first few flights.
SW