Sometimes “NSFW” (not safe for work) is also used to warn you when something is going to make you laugh way too loudly in the office and attract a lot of unwanted attention.
Even if the company doesn’t monitor you through software, you don’t want to be viewing NSFW content when a boss or colleague walks up behind you. It’s also a good idea to avoid anything marked “NSFW” if your children are watching.
@Bluefreedom, that’s so, unless, of course, the Fluther question happens to have been marked ‘NSFW’...