Would sinking the battleships in deep water have cost Italy more?

Would hitting the Italian battleships in deep water have harmed the war effort more than sinking them in Taranto harbour?

Possibly, but a harbour strike that left ships beyond repair could also drain Italian salvage and industrial resources without letting them return to service.

A deep-water sinking could deny Italy the option of raising a damaged battleship and might have imposed a larger final loss. Harbour salvage, however, consumed scarce time, labour, and industrial capacity. From the British perspective, the ideal result was to strike the concentrated ships where they were and damage them beyond useful repair. That would combine immediate operational shock with a prolonged demand on Italy's limited repair system. The tactical image of a ship sinking is only one part of the economic cost of trying to recover it.