The ‘Tracking opt-out reason’ dimension acts as a preview to data that would be excluded if you enabled Privacy Settings. This dimension is primarily used to determine if your implementation would be negatively impacted if you enabled Privacy Settings under Report Suite Settings.
Typical implementations see 1% or less of their overall report suite traffic under this dimension if Privacy Settings have not yet been enabled. Percentages higher than 1% of all traffic suggests a potential implementation problem that prevents AppMeasurement from setting first-party cookies.
This dimension works out of the box for all implementations that have not yet enabled Privacy Settings. If your organization has already enabled the Remove users who have blocked all cookies setting for both desktop and mobile browsers, this dimension does not contain data.
Dimension items include
"Cookies disabled by Desktop Browser" and
"Cookies disabled by Mobile Browser".