This allows cross-device tracking, i.e. tracking across multiple devices, and offline tracking. With cross-device tracking, the data of your online behavior on different end devices (e.g. PC, smartphone, tablet PC) can be linked. Offline tracking includes tracking of, for example, your visits to offline shops. Both is only done if you have enabled the "personalized advertising" option in your Google Account settings. You can activate and deactivate the option "personalised advertising" at any time in your Google user account.