A luhtier friend of mine recommends brass pins when the brightness of tone is lost after, say, shaving the bridge (reducing its mass) to delay the need for a neck re-set. The older amongst us will also remember the fashion for replacing bone nuts with brass. Basically, its all down to wight distribution. If you add mass to the head of a guitar, it changes the sound, increasing sustain. The simplest way of doing this is to add a G-clamp to the head. Similarly add weight to the bridge and you change the tone and sustain. Brass bridge pins are probably the simplest and most elegant solution.