Can be used together to analyse web traffic and to gain an understanding of the performance of ads.
Google says the service is combating the many new accounts users need to make for websites they want to access. Whenever a website visitor is asked to sign in, they are offered the option to create a new account. To a lot of users it seems time-consuming and tedious, and the alternative is to sign in through their Google account. Google Identity Services then shares the user's name, email address and profile picture with the website owner .
However it also means that Google gets the information that you are signing up to a specific service or website through their identity services. Users also need to interface with the website owners through the Google API, sharing information about login times and website activity with Google. This allows Google to create more in-depth analysis profiles of their users, because it gives them access to data disclosing what websites users visit, how often they visit them, and for how long. This data is used to train their advertising algorithms.
Google is offering a simple way to sign in and through this service, they gather much more data about internet users. Providing convenience to users, further cements their position of power. Google retains information about users comparable to a private investigator's level of knowledge - very invasive.