Our org was upgraded to winter '18 this weekend. The black global header is now viewable at the top of Classic for all users. This was not the case before the upgrade. All users have the 'View Global Header' permission ticked but this wasn't changed during the upgrade (they had it ticked before). We used to use communities but no longer do. My understanding is that deactivating the last active community was what made global header previously stop displaying.
Does anyone know what changed in Winter '18 that would cause this change? I can untick 'View Global Header' in all profiles but want to understand the root cause of the issue first. Are there any potential unintended consequences for unticking the box?