Shape and Definition: It can help you define the edges of your lips for a more polished and structured look. Preventing Bleeding: Lip liner is a barrier that keeps lipstick from feathering or smudging outside the lines. Longevity: A lip liner can help lipstick stay in place longer by creating a base to adhere to. Enhance Lip Size: By slightly overlining the lips with a lip liner, you can create the appearance of fuller lips.