Do I need to decline cookie prompts if my browser automatically clears cookies?

Continuing the discussion from Automatically deal with cookies pop-ups using Consent-O-Matic extension:

The problem here is that “declining cookies” on a website does not really guarantee they’re not sending you cookies. Cookie prompts are merely an agreement to not save cookies to your browser which isn’t technically enforced, and you’ll note that many of them say they’ll save “necessary” cookies anyways.

The only way to be completely sure you’re avoiding tracking cookies is to clear your cookies regularly as @matchboxbananasynergy suggested, since that is an action your browser does which can’t be interfered with by websites.

You still deal with the problem of cookies that you get during your current browser session, before you have a chance to clear them. This is where a solution like Multi Account Containers might come in handy, which lets you contain cookies to only certain websites.

Another option (esp. for Chromiums) is to open links in a new Private Window. This will discard anything stored locally after you close that window.