What if you have a fairly weak weapon, let me make up some numbers, with a damage track something like
3 2 1 1 0
If all the weapons can fire in the same arc there is no negative modifier so it will do 3 damage and still do 1 damage if the ship is working under a -2 penalty due to having taken weapon damage.
If the weapons are split up and due to this have a -2 penalty, then when they take the -2 weapons penalty, are rendered useless because they do 0 damage now.
Thus, I would think you would not want to split your weapons into too many banks.
On the other hand I can also see how rounding might give you an extra dice of damage at times. If the above weapon had 4 turrets with a 2 or 3 adjust, you could get a total dice output of 4 dice rather than 3. It might make a difference if you can get all those weapons to bear but if they point in many directions, it's no advantage.
So... I would say that split banks confer a slight edge (sometimes) in the early game, but as a ship takes damage that gives him firing penalties, the multiple banks becomes inferior.
Both are small things though, and only a real numbers nerd would have thought of them. Ehem.