Upcoming features and services involving third-party and ad-supported content will require Plex to collect and, in some cases, share information about the third-party content you are streaming. For clarity, third-party content is content that we deliver or stream to you that is not contained in your personal media library.
Plex also goes into some detail about a change it has made to statistics collection. No longer will users have the option to opt out of the data collection, noting that Plex does not share or sell the data outside the company. Perhaps more important for some users, the service does not collect data around the libraries, file names or any content-specific data on your privately hosted servers.