When choosing salvo or not I think you have to make a distinction between wanting to improve your hit accuracy, or increase the change for hitting something at all. If you want to learn torpedo aiming (manual targeting) or improve your accuracy in TDC settings then you should not fire salvo's. The slight angle that the torpedoes veer off from their base course disguises the feedback you receive from the torpedo-cam or freecam. It's difficult to get a feel for how much that salvo angle corresponds to a position along the target length at different ranges and AOBs. You'll never get a clear idea how much you were wrong with your aim. I suppose if you fire 3 torpedos then the middle one would be able to confirm the accuracy, but 2 definately limits your learning efficiency. The second reason is that instead of 1 attempt with 2 torpedos, you can try 2 attemps with one torpedo. More tries in the long rung(Or 3 if it is a triple-shot) Salvo's can waste torpedos quickly. Often just one torpedo is enough to cause fatal flooding. Why be pre-emptive with more?
However if it is more important for you to get any torpedo impact on the hull, instead of a torpedo on a specific location of the hull, then a salvo is more appropriate. But you'll have to do the mathematics of how wide the target is at that range and AOB, and set your salvo angle accordingly. Just setting a rule-of-thumb angle is unwise. Unless you fire from point-blank range. Then nothing matters.
Personally, I never fire salvo's. I'm always in learning and feedback mode. And a cheapskate.
