Confession is a Sacrament. It gives us graces towards our eternal salvation.
One could still argue, why involve the priests, why not do it directly with God. Why do movie stars and athletes have personal trainers and someone dedicated to manage their nutrition? Why don’t they do it alone, can’t they take care of it on their own? I think the answer is pretty obvious: their trainers and nutritionists keep them on track much better. The same thing goes for the involvement of priests, confessors and spiritual directors in our lives. They are there for us, and they keep us on track on our journey towards sanctification.
I wouldn’t take the place of a priest who hears confessions. I mean, the part of listening to other people’s sins again and again, and comforting and exhorting, strengthening them, should be pretty tiring and not particularly enjoyable. But the ability to give absolution (because Jesus Christ specifically gave this power to the apostles) must be awesome!