Dialing in the accuracy of your miter saw won’t keep the blade from tearing out at the bottom of a cut. I’ve used scrap pieces beneath the cut and have also added a sacrificial top to the saw’s table using ½” MDF. But both approaches are less than ideal, especially if you’re cutting trim of multiple widths and thicknesses.
Brian Way always has an insightful way of doing things, and often finds a lesser-known product that is worth noting. In this video, Brian shows how to use a zero clearance insert from FastCap. He also points out an added benefit toward the end. He installs the tape on his Festool miter saw, but the product works on any miter saw.