Google Analytics is tapping into first-party data. As Josh Silverbauer posted, Google has announced in the latest update its intention to utilize user-provided data for user identification in GA4, even without the transmission of a user_id. In other words, inputting the same email in forms across different devices will link these users together, despite having different client_ids.
The intent is clear – amid the tightening regulations on third-party cookies, vendors are seeking more avenues for legitimate user identification. However, the implementation, as usual, is lacking. I've previously mentioned how enabling the user-provided data collection option can adversely affect the transmission of user_id to your BigQuery export.
Furthermore, this mechanism operates on a sort of parameter hierarchy – email, followed by phone, then name, and finally address.
If you work with GA4 to BigQuery exports, be sure to check out my SQL cheat sheet.
