Making high quality circles (especially small ones) is difficult with a compass. A circle template allows circles to be constructed with lead holders and mechanical pencils. A circle template is a plastic tool that has been perforated with round holes of various diameters. The holes are oversize by a small amount to accommodate the pencil width. Even large circles are better drawing with circle template if the correct hole diameter is available.
Templates are available for many other common shapes including ellipses, bolt heads, architectural symbols, and more.