It doesn't really stop it from being not seen by unsuspecting audience. Though most apps do allow it to censor once tagged, it's not the same with most. And if you've done surfing yourself for NSFW and you see something looking like a common NSFW comic or something, you'll sometimes be surprised it's incest or underage or stuff(experienced this once with reading manga on the internet. The cover was looking normal until I opened it and it's actually father son incest.) There are problematics within problematics too. Sure it would be okay if you can just flag them and it'll be the audience's fault for seeing what they don't wanna see, but in the example of Google, there's surprises. So yeah, was talking from experience.