I have heard numerous times on the forum that the function of the kilt pin is to weight down the front apron. I suppose this may be true only if one is wearing an extremely light weight kilt (or has a rather large and heavy kilt pin!).

However, if one is wearing a traditional kilt made from even medium weight cloth, and wearing a typical kilt pin, which may only be a few ounces at best, the amount of weight added to the kilt apron is really insignificant.

Plus, that implies that there is a "need" to weight the kilt apron down, which there is not. Unless one is wearing a kilt made from an extremely light weight fabric, the weight of the cloth itself should keep the apron down just nicely in anything but the strongest of winds (when that 2 oz kilt pin wouldn't help at all anyway).

A kilt pin is purely decorative, and a matter of personal preference as to what style or how to wear it.