I think the the combination of physical tasks and mental tasks, and sometimes the choice between the two allows for a wider variety of racers to be competitive, because those who are good physically may not be so good at the mental tasks and vice versa. That way we don't just get the most physically gifted teams always way ahead or winning.
However, if the physically gifted teams are given the answers to the more mental tasks and therefore don't have to preform them, that gives them an unfair advantage. The more mentally gifted teams can't have the physical tasks performed by others for them, so I don't believe teams should be able to be given the answers to challenges either.
I like that we can have different age groups and abilities competing together, but the answer sharing threatens to eliminate this.