A client ID is a unique identifier. When you visit a website or web application that uses Google Analytics, you get assigned such an ID. The client ID is a randomly generated string of characters stored in a cookie on your web browser. It is used to link together all the interactions you perform as a user with a web page over time.
Within Analytics, the client ID is important because it allows a platform to track and analyze individual users’ behavior across multiple sessions and devices. Without the client ID, Google Analytics would only be able to track and analyze behavior per session. This would provide a limited view of users’ engagement and interest in the website. So the client ID is a perfect way to gain more information.
You can access and analyze the client ID through the User ID feature in Google Analytics. This feature allows you to enable the tracking of the client ID and to access the data and reports that are based on the client ID. This also includes reports on user behavior, such as the number of sessions, pageviews, and events attributed to each client ID.