Ask HN: How to use vouch feature?

I have showdead on, and I see a lot of links that are not necessarily spam, and have somehow been marked dead. Here's an example [1] This link is not really spam, but not something I'm particular interested in. So, I'd vouch for it but I'm not going to vote it up.

Should we be using vouch to say "this is not spam"? Or "I know and trust the submitter"? Or "this is a good link"?

Does vouching for something decrease some internal karma? Should I "save my vouches" for something that is really important?

[1] https://news.ycombinator.com/item?id=14471231