If your plans go awry for some reason, you can use a friend as a convenient scapegoat.
This “fall of the favorite” was a trick often used by kings and sovereigns: They would let their closest friend at court take the fall for a mistake, since the public would not believe that they would deliberately sacrifice a friend for such a purpose.
Of course, after you play that card, you have lost your friend forever. It is best, then, to reserve the scapegoat role for someone who is close to you but not too close.