You are the 4rth blue droids. You were the first unit in the battle and you already hitted a green unit once. You know that if 4 more rounds hit the green unit it will die. What will you do on you second shot 5 second later ?
You an me would take a second shot on that green unit. Assuming we have god like intelligence and we have all the time to analysis that situation between exactly 2 shots, we would deduct that that even if all the blue and the red units shoot at that green it would most likely survive (about 55% chance) so there would be no reason at all to change your target on that shot.
But not if you are a 3.1 droids ! Not only the 3.1 droids would know where each red unit shoted, but they would also already know the issues of the cannon rounds that are still in the mid-air ! They would know exaclty (even in a gigantic battle field) how much bullet in mid-air will make damage to any units and they would base their target on that prophetic knowledge.
![Annoyed :annoyed:](./images/smilies/icon_annoyed.gif)
I believe it's a HUGE balance issue, it increased seriously the DPS of the units in the game as they barely never use a single shot more than necessary with a prophetic knowledge of the projectile still in mid-air.