Keep in mind that this is an “all or nothing” setting at the moment, meaning that if you set “21+” it applies to all your posts regardless of the content. Same with if you restrict based on location. That means the benefit of this option is more for groups/businesses than individuals, though I’m sure some individuals will find this useful as well. Google’s Yonatan Zunger does indicate that per-post controls are already “on our requested features list”, so eventually G+ users may have the power to hide only specific posts that wouldn’t be appropriate for younger audiences.
With new options for 18+ and 21+ age restrictions, we also have to wonder if Google is toying around with the idea of being more lenient on its censorship policies for those who restrict their content to older audiences. For Google’s part, they say they aren’t changing policies at this time though they admit “this does give us some flexibility to do that”.
[Source: Android Authority]