Well if you have ever been a backbencher then you would get my answer.

What do the backbenchers do-

You can literally do anything you want except for making noises.You eat while in class,you throw paper balls to your friend sitting ahead of you.You use smartphones and earphones. Teachers can hardly notice the backbenchers using these gadgets since they cleverly use it.You talk with friends very silently sometimes through murmurs.Sometimes you get caught doing all this.

The fun part -

The fun part of being backbenchers is that you live your school life close to how you want.Often teachers know its no worth everytime to insist backbenchers in answering the questions or scolding for not submitting homework or staying quiet in class and so you get an indirect support from teachers as well since they get used to you.Its not always that backbenchers dont have to submit homework or they are not regular at completing their class tasks/homeworks.I have seen many of the backbenchers getting top ranks in class. So if you are of the opinion that being a backbencher will lower your grades then you are wrong. So basically being a backbencher you may enjoy more than others sitting ahead of you. Its not obvious but this is a well observed fact. So along the time since you are enjoying as well you may make some real friends who will always be with you in mischiefs and punishments too and you are going to miss these punishments,mischiefs your backbencher guys for the whole of your life.

I think that is why backbenchers are important.