Different witches and wizards are born having different amounts of the five elementals, and these amounts will change based on learning and usage. The power of a spell a mage casts depends on the elemental of both the spell and the mage. Thus, one mage may be able to cast excellent fire spells and yet have difficulty casting water spells, while with another person the situation may be reversed. Although most magicians prefer to cast light spells, dark witches and wizards are drawn to Darkness and want wands that excel at casting dark spells.
Finally, some wand components work best with witches, some work best for wizards, and some work equally for both witches and wizards. The gender of the components needs to be consistent with the gender of the wand's components.