Here is Google’s advice on when you need to submit your sitemap

There is a term which everyone must be aware of when handling a site or even managing a site as owner. This term is a sitemap which should be there for every website on the internet. A sitemap is basically a txt file where all your links of the website are clearly mentioned so that the Googlebot can crawl each of your pages and their articles easily to index inside search. If you are submitting your website on Google Search Console, you will be told to submit your sitemap. This is to make sure that Google’s crawler finds it easier to visit all the links on your site.

Also, there are problems that occur when the sitemap shows links which are not available on the site due to removal or other reasons. Therefore, it is always recommended to update your sitemap. But if you believe that Google does not crawl your website if you don’t have a sitemap then you are wrong. Because Google’s John Mueller says that the search engine can crawl your sites even if no sitemap is there as long as all the links on your site are properly visible.

However, there are certain times when a sitemap is required. Google says that if your site is small with limited links, the crawler will index them easily. However, you will need to provide a sitemap if your site is huge with a massive amount of links. Also, if your pages are isolated meaning that they are not interlinked then you will need a sitemap as well.

Apart from that, you also need to provide a sitemap if your site is new on the internet and also if the content on your site changes quickly meaning that you are posting frequently on the site. Having said that, Google says “it will not always crawl every URL included in a sitemap”