Why incendiaries offered little at Taranto

Could Fleet Air Arm aircraft have used incendiaries to ignite oil in Taranto harbour?

Potentially, but the extra fire would have offered little operational gain while destroying small harbour craft unnecessarily.

British aircraft might have been able to ignite oil and other flammable material in Taranto harbour, but the result would have offered little operational value. Once the Fleet Air Arm was attacking the battleships, setting the surrounding water ablaze would have shifted destruction toward small boats and support craft. That additional violence is described as unnecessary and inelegant rather than a worthwhile extension of the raid. The torpedo attack already served the operational purpose.