The system strain of ANYTHING more or less would not be negligable on low end machines.. and it IS strictly an aesthetic thing. So articulated turrets can be optional.
I just think its just about the worst visual blooper you can do when you can reach a situation where a cannon is visibly aiming one way and a shot firing another.
You don't need any distance calculations or anything.
Just the turret to align in the direction of the shot which is already calculated.
as soon as a ship acquires a target, its turrets animate to turn towards the target, then when the animation is done, they start firing.
If the turret animation takes 1-2 seconds, then its of no consequence to the game either and strictly aesthetic so no problem.
Also, as said, it would only need to animate on VISIBLE turrets, which aren't bound to be THAT many.
But it could also potentially add tactical depth.
If the turret movement is relatively slow, it adds another deep element of tactics, since it would encourage you to manouver your ships more smartly to keep them firing in the same general direction to minimize turret move time, and would encourage you to manouver your own ships out of the enemy firing lines.
This would in effect make all tactical manouvers more powerful (surrounding an enemy, for example, would be more beneficial, because all turrets would be turned to the center of the ring at all times and require minimal movement to focus-fire on a target, while the units inside the loop would all need varying ammounts of time to syncronize in order to focus-fire)
I think it could actually add a lot to a game like this, and generally, it DOES make sense that it would take some time for cannons as insanely huge as starship cannons to pivot and turn.
Another part of it is that really, really huge cannons (the ones that are just too big to be placed on turrets.. basically a ship built around a cannon like that ship in homeworld) have a mobility disadvantage.. I dunno, its all tactics.
Depends somewhat on the focus of the game.
I think in a good RTS game there should be a big element of tactics to make battles exciting. It's just not fun to simply make a lot of units and send them around the map and forget about them.. there's a lot of fun inherent in directing your ships movements and manouvers, AND HAVING THIS EFFORT PAY OFF (the important part), as easily demonstrated by games like starcraft/homeworld/etc.