What is the real use of the NSFW qualifier?

Thinking on a question @bobbinhood asked about the use of NSFW qualifier it made me think what real good is it? If there was a NSFW question what would not stop minor Flutheronians from viewing it? There is no software or cookies that would block them or give them a 401 Forbidden page. If a video store that has an ”Over 18” adult section in the back but no one watches the door and anyone can come and go as they please how useful is the sign? If it is just there to say to people “don’t open it where your boss or coworkers can see” then it does its purpose if it is to do more than that I don’t think the success rate will be anything to brag about.