Google's crawlers discover pages mainly by following links, and pages that nothing links to may never be crawled at all. Google's own explanation of how Search works describes crawling as the first of three stages, and the majority of indexed pages are found automatically rather than submitted in the in-depth guide to how Google Search works. The practical consequence is simple: if you publish a new page and no existing page links to it, you are relying on the sitemap and luck.
Internal links do a second job beyond discovery. They tell both readers and crawlers how your pages relate, and they help spread ranking signals from stronger pages to weaker ones according to Moz's internal links guidance. Google's link documentation puts it plainly: it uses links as a signal when determining the relevancy of pages per the Google link best practices page.
That is why planning links before publishing is cheaper than repairing them after. Once a page is live, adding a link means editing another page, re-checking its layout, and often editing a template you were not planning to touch. Deciding the link at draft time costs one line in a map.
The goal of the plan is not maximum links. It is a link structure you can explain. Google's starter guide frames the whole discipline around making your site easier to crawl, index and understand, with organization and descriptive URLs as part of that work in the SEO Starter Guide. A link map is the smallest artifact that keeps that organization visible while content volume grows.



