Most of the good rocket launchers have tracking. That's all there is to it. Let's say I have two identical rocket launchers, one with tracking and one without. You would be foolish to not take the tracking one. Let's say the top launchers are gjallarhorn, hunger of crota, truth, and dragons breath. 3/4 have tracking. We don't choose if it has tracking, we just know that if the rocket launcher is good, we're going to use it. Simple