Many people walk through the world carrying burdens that have been paced on them by the choices of their family members, not just in this life but from the families previous mistakes.
Ancestral healing allows the healer to look through the number of family members you have and narrow down who it is in you family that has caused your present predicament and deal with the problem by either talking to the person on solving the problem that they encountered that caused the clients present problem.
In some cases this may just be acknowledging the person exists and thus removing the resentment by that person from the family energy. In other cases it requires a bit more of an effort by the healer to the point of shamanistic journeying to face the person head on and request they move on to the spirit world rather than remain and torture their current living relatives.
All require a strong trust in the divine and the healers guides as well as confidence in themselves.