All depends on what distances you shoot and how accurate you are, or how good your form is. Most I have seen shoot recurve cant the bow, I think it has something to do with keeping the arrow on the shelf while drawing and holding. Not sure because I don't shoot traditional.

It really doesn't matter what you do, as long as you do it the SAME EXACT way every time. If you cant the bow on one shot, and then don't on the next it will change the impact point of the arrow. The farther the distance, the more it will be off. Using a level helps keep the bow the same for every shot.

Do you need one? No, I don't even use a peep sight most of the time at hunting distances let alone a level. However if you are trying to be the most accurate you can be it would certainly help. Unless you have perfect form from shot to shot.

Paul