I have never completely bought into the idea that the Sgian dubh was a "weapon of last resort". From the very shape of it, it looks more like a utility knife one would carry for a variety of uses.

Also remember that until the industrial revolution, cutlery was very expensive, and when a guest arrived, it was usually expected that the guest would furnish his own.

I feel that at a formal occasion, it is necessary, just part of the "traditional" dress. At other times, as the occasion demands. Just wear it far enough down into the hose so it can't fall out!