What type of data does Google Analytics prohibit you from collecting?
Personally identifable information
The Google Analytics terms of service, which all Google Analytics customers must adhere to, prohibit sending personally identifiable information (PII) to Google Analytics. PII includes any data that can be used by Google to reasonably identify an individual, including (but not limited to) names, email addresses, or billing information.
Read more here: https://support.google.com/analytics/answer/6004245