Google has user accounts that allow a user to streamline accounts through all of its services, including Gmail, YouTube, Google+, Google Maps, and many others. Accounts with Google mine data of almost every aspect of a user's browsing habits, as well as data about their location and other aspects of their lives.
Search Engines like Google and Bing state that they store this information to personalize the web browser. Creating a custom experience for each user. Searches within the engine are more accustomed to previous searches on the users account. It is true that this can be helpful in creating a search engine which is personalized for the normal patterns of a User. However, the data generated by these accounts are generally used for advertising purposes, allowing advertisements to be tailored to specific individuals. Using Artificial Intelligence, a website like Google or Facebook can create custom advertisements based on your interests.