What Exactly Does the Crawler Do?
Your website is its own network of different pages. All these pages need to connect to each other (and to the outside world) for both users and search engines to correctly see it. For example, if you create a new blog post and within it, you try to create an internal link to a page on your site and have a typo in the hyperlink then you will create a broken link.
If you are posting content regularly, it is easy to forget about checking all your links, but just a few of these small mistakes add up because it makes your site look disorganized both to users and search engines.