tags that apply to some content vs tags that apply to the purpose or subject of a site

So, is the tagging supposed to be

"this tag applies because I found content on this site that applies to this tag"

OR

"This tag applies here because this is the subject or main goal of the website"

I'm asking this because I'm seeing a bit too much sites I feel are wrongly tagged because they contain a few pages of content (usually user-generated) that is not the main subject of the website. And I flagged for review a couple of them because I think websites should be tagged by their subject/main goal/focus rather than part of their content that has nothing to do with it in the first place.

So which is the good way of tagging ?

This is why tags are up for voting and a final approval/rejection, and open to being flagged after.

I mean, it is better not to tag a whole domain for a few minor items when the rest of the content does not fit. But if there are whole sections of content fitting a category, the category may apply.

The best method I can suggest is to imagine that a domain was blocked under some category, and decide whether you would find this helpful or annoying. Then consider how other users might see it - are your views fairly extreme? E.g., would you block a whole domain as Bikini/Lingerie because someone posted a picture of their family at the beach? That would be a bit extreme.

Domains don't necessarily have subjects, and filtering here is domain-based. So use keyword or whatever filtering on your router or by using an installed application.