Answer: No, but if you do not, your page will show up in results without a brief description to help visitors understand what the page is about or contains.
Answer: A teaser is a short, summarized description of the page's content, usually one to two sentences. This description appears in two forms; after the link title on a results page and on the display screen as a tool tip - a small "hover box" with information about the item being hovered over with a mouse.