Ancestral skills permit you to select between two versions of three available skills in the trees. They are very useful in their own way. It doesn't give you anything else. For the majority of the trees, you should be using at least one of the skills provided. From the three classes I rotate, I use ancestral skills from Vitalism, Auramancy, Defense, and Songcraft. The list is limited, but you should still be using them if they're recommended by those who play the class(es) you do. What else would you be looking/wanting from Ancestral skills?