Edgers and bevelers are tools used to shave the square edges off of leather. This is both for functional and aesthetic purposes. Functionally, it removes the sharper square edges and leaves a more rounded edge to the leather. This makes it less likely to catch on to other items during daily use. The rounded edges are also more comfortable on items that are handled frequently such as belts and wallets.
Aesthetically, the rounded edges on leather are generally more pleasing to the eye. They soften the look and also make it easier to seal the edges when they are burnished or edge-painted.
Edgers and burnishers come in many different shapes, sizes, and styles. They are usually made with metal blades/tips attached to a wooden handle. One thing to keep in mind is that not all edgers are sized in the same way. A particular size from one brand or manufacturer might not match that from another manufacturer.
Similar to clothes, it’s best to try out the ones you’d like, and ensure the sizing meets your needs. In general, it is important to keep the edges sharp to ensure smooth, clean cuts.