The melee attack is a excellent way to save ammo. It is useful in easy and normal mode, and works ok in heroic and legendary. The three main targets of a melee attack are; Jackals, unshielded Elites and Grunts. Two hits from any melee attack will kill just about any Jackal, with or without a shield, as you run up to them they will attempt to back away, as they are backing up nail em'. To use it against Elites, take out thier shield with a AR volley or Plasma Pistol burst and while they are stunned whack them, about 2 hits should do it. Don't try it with a sword wielding Elite (unless you have a death wish). Grunts are a no brainer, just stroll up to the weaklings and beat them silly. One or two hits should do it. If you can sneak up on either a Grunt, Jackal or Elite, then by all means melee them, it also helps if you have the Active Camo power-up. Just make sure you smoke it while you got it.