User ID is an underutilized capability of the Universal Analytics version of Google Analytics. It offers tremendous potential to improve your business, especially if you sell to businesses or are highly dependent upon repeat customers.
User ID is aptly named, as it allows website owners to Identify their visitors in Google Analytics. The User ID dimension is a unique identifier that the website owner can assign to individual users. We all know Google doesn’t allow Personally Identifiable Information in Google Analytics. That being said, a string of apparently random alphanumeric characters is allowed in the User ID dimension and that string could represent a hashed version of a customer’s email address or more practically, a customer’s account number or account ID from your website back end.