Reviewing answers, I recently experienced the following workflow problem:
There is a late or first answer and when I click "review", I get the complete question (but without tags, which is a different topic, but in many cases a vital information - think regex in Perl, sed, Postgresql, Python, ... with the subtle differences).
But I find fine answers, and would vote them up. But I got suspicious, that such an answer hasn't been posted before - for old questions though, but even for new questions, experienced users are normally faster.
So I middle-clicked: open in new tab, and there I could see, that other answers already gave the same advice in other words, often upvoted and accepted.
So in this context, another valid answer is just noise and traffic. I used the opportunity to make a comment, that we don't need duplicated answers, but it is not comfortable to find this information, as a reviewer.
I think, we need nearly always the whole thread, except if the answer can be clearly judged as false or spam. Having all the information at hand at once would encourage to look for the answer in the context.
Maybe the review can be more sensible, and only show the answer in context, if there is already an upvoted and accepted answer.