Critiques or praise only?

I haven't noticed any critical feedback on work posted on the site. This might be because I haven't looked hard enough, or it could be because that isn't the purpose of this site.

Before I do something that might be totally out of line, could you tell me if constructive criticism is encouraged, or do we only comment on work that appeals to us?

My reason for asking is that I believe, to grow as a writer, we need to know what doesn't work, as well as being praised for what does.

Even some of the cherry picked items have flaws that, if pointed out, would help the writer to improve and move to a higher level.

I'd appreciate having some guidance on this.