When a visitor accepts to the cookie consent they are agreeing with the terms and conditions of your website tracking. This means they allowed their online journey on your site to be tracked and that information be used as per your terms. For example you could be subscribing their emails to a marketing list.

If a visitor ignores the consent banner it is considered a consent. They did not actively decline the cookies. Maybe they have a misunderstanding of what it does when you don't make any decision? It's now implied consent and are treated as if they have accepted cookies. 

Learn more about Cookie Consent, here.