Depending on what I am making, I usually glue the paper to cardboard, mark the leather with the exact size but cut out most parts with an additional 1-2 mm. After gluing, I cut to the exact size. This helps immensely to get sharp edges for the edge finishing process. For example, when making a wallet, I leave space on the sides of the T-slots, and side and bottom of the T-slot cover. When I am happy with a template that I made, I will re-do the template and include the additional 1-2 mm where needed and keep the original template as a cutting guide.