If you're unsure whether or not you need a sitemap, it's important to know about the two different kinds of sitemaps first. There are HTML sitemaps, which are actual pages on websites that list all of the pages on the entire website, typically appearing in sections. XML sitemaps include the same listing along with a little more information, but are only visible to search engine robots.
Despite not being as important to search engine crawlers as XML sitemaps, HTML sitemaps do serve a purpose. Even if you get less than one percent of traffic directed toward this sitemap, you can still benefit from that depending on how minimal your website's traffic is. Sitemaps also give visitors an easy way to navigate your website, helping them find pages that might otherwise be difficult to find via the homepage.
XML sitemaps are needed to make it easy for search engine robots to crawl your website, making the process of indexing and ranking new pages simpler and faster. You'll need XML sitemaps if your website has dynamic content, has very few or new links, or if you have a lot of pages with high-quality content that don't link to others. You can even use these sitemaps to help guide search engines, providing them with info regarding how frequently the pages are updated, modification dates, and the importance of each specific page.