This feature is very useful for forums with controvery content (violent, adult, "offensive" etc.) content. This safemod is a button, if you click on it you can disable the view of several forums and disable the view of is topics on what's new and recent activity. An example can be the filter of 4chan.org (you can see only the worksafe forums).
I've seen this feature on video sites, unfortunately, I don't think it's something that belongs in the core product. I think you'd be better off requesting it on the modifications request forum. I like the idea, but it's just something that doesn't belong in the core. IMO