Cutting slits in chicken breast serves the practical purpose of ensuring even and quick cooking. By making shallow cuts through the thickest parts of the chicken, you create separate and more uniformly sized sections. As a result, the thicker portions of the chicken cook at the same rate as the thinner areas, preventing uneven cooking. This is especially beneficial when grilling, pan-searing, or baking chicken breasts, as it helps to avoid undercooking or overcooking certain parts.