Often leave you wondering why you can’t click anything on the page
When I click "I agree" I am not agreeing to cookies but rather to tracking. If the website wants to track me with (say) browser fingerprinting, deleting the cookies will not stop them from tracking me across sessions. Even worse: since I agreed they no longer need to show me a warning, so I may not even notice that I may want to revoke that consent.
If I don't want to be tracked, saying "I do not consent" is the only legally-actionable way. Deleting cookies works now because cookies are still cost-effective, but this won't remain true forever.
> In most cases, the add-on just blocks or hides cookie related pop-ups. When it's needed for the website to work properly, it will automatically accept the cookie policy for you (sometimes it will accept all and sometimes only necessary cookie categories, depending on what's easier to do).
It’s usually “we value your privacy”, which always makes me think “you put a value on it, alright, can’t wait to take it away”.
¹ The GDPR is clear that rejecting must be as simple as accepting.