It's a benefit only in terms of publicity. In the same way if someone killed someone with a knife and left a "Jack the Ripper was here" note would get a lot more sensationalistic press than no note.
Anonymous was a household brand name during Obama as they were exposing a lot of what he was doing behind the scenes, like drone strikes on innocent civilians and illegally targeting Americans overseas without due process. It was in the news constantly with their videos at a time when most people still watched TV.
