The advantage of hearing both sides of an argument is that you would have a better chance of forming an unbiased opinion. It would also help you have a stronger argument for adopting a position on an issue, because it would be based on more information. And as you would be well-acquainted with the arguments on both sides, it would also help you defend that position against attacks.
More importantly, it would allow you to change your mind in order to accept new ideas, because it would make you open to listening to better, stronger arguments, regardless of their origin.