The two main ways ads have of tracking users are: * Cookies: ads ask the browser to store something, later they can ask what the stored value is. * Fingerprin

The two main ways ads have of tracking users are: * Cookies: ads ask the browser to store something, later they can ask what the stored value is. * Fingerprinting: ads collect enough information about the browser that they can distinguish it from other users' browsers. While cookies aren't ideal, I think an ad industry that uses them is a lot better than one that uses fingerprinting. The key differences are user control and visibility. If you clear your browsing history, or close an incognito tab, your cookies are gone but your fingerprint is unchanged. Similarly, you can see who's setting cookies but you have no idea who is trying to fingerprint you.