This immunizer disables the Diagnostics Tracking in Windows, also called Connected User Experiences and Telemetry.
Microsoft describes it as:
The Diagnostic and Telemetry service collects diagnostics information about functional issues on Windows systems that participate in the Windows Customer Experience Improvement Program (CEIP). CEIP reports don’t contain contact information, such as your name, address, or telephone number. This means CEIP won’t ask you to participate in surveys or to read junk email, and you won’t be contacted in any other way.
It is required if you want to use the achievements system in some Windows games. If you do not rely on this feature, we recommend to disable this option.