"No result" is what investigative roles receive for their action if they are roleblocked or similar. While in the majority of cases players are not informed that they have been blocked, if the player is expecting a result, it is terrible form to simply not tell the player anything (they may assume the mod missed their action or forgot to give their result). Therefore it is necessary to tell the player they obtained no results from their investigation.
It should generally not be possible to obtain a "no result" when not blocked; if a role learns that nothing happened, that's not a "no result", it's a result of "nothing happened". For example, a Tracker should be told that his target did not visit anyone, and a Watcher should be told that his target was not visited by anyone. Giving "no result" in these situations is ambiguous and not normal.