as others have said they can be used to help remember stuff like log-in status, but also stuff like what you put in your shopping cart if you leave and return.

Now you also mentioned tracking, and yes, thats why you are asked to accept them now. websites and marketers use cookies to track all kinds of things about who you are, where youve been, and what you do so they can target ads to you. This can be info like where you are located in the world, in your country, even in your state. What OS you use, what browser you use, the size of your screen. And if you log into the same sites on your phone then they get all that info too.

There have been massive lawsuits about the dossier different companies built using these tracker cookies and even today it is very difficult to remain truly anonymous online because everything is tracked, legally or otherwise.