If the answer is not community wiki, which _invites_ such edits, then I reject them. The usual reject reason I use is "radical change".

![radical change][1]

[A suggested edit I just saw in the queue][2] makes a great example. This was completely new content that was different and unrelated to the existing answer, and should have been posted as its own answer.

The person who originally posted the answer may have had a reason for not including the content, other than not knowing about it. Such edits cause the user's answer to be something significantly different than what the user intended.


  [1]: https://i.sstatic.net/YMCvu.png
  [2]: http://serverfault.com/review/suggested-edits/136164