The critical role is if something goes wrong to be able to help the passengers be safe. E.g. non-normal landings and medical emergencies. Another less "critica

The critical role is if something goes wrong to be able to help the passengers be safe. E.g. non-normal landings and medical emergencies. Another less "critical" role, but still not something I want a pilot doing, is dealing with disgruntled passengers. They also ensure that rules are followed and that people, e.g. in an exit row, understand what they need to do. If pilots couldn't begin preflight until passengers are seated and buckled it would take forever to depart. Speaking of boarding, flight attendants also deal with seating and baggage issues. Again, it would delay departure.