An effective information architecture is critical if you want search engines to be able to find your content and serve it to users. If crawlers cannot access the content, they cannot rank it well. From a human point of view, information architecture is important so that users can easily find what they are looking for.
At a basic level, a successful information architecture ensures that all of your pages are linked in a way that allows search engines and people to read all of the content on your site and move between those pages effectively. It also helps search engines prioritize your important pages for ranking purposes.
The speed at which users can find what they are looking for is normally a sign of a good or bad navigation; in the SEO industry, we tend to relate this to the number of times a user needs to clicks from the homepage to find the product or service they are looking for. Pages that are fewer clicks from the homepage are sometimes referred to as ‘money’ pages, as they are normally where the final call to action happens. These pages also receive the most link equity so that they have a better possibility of ranking well for competitive terms.