Dedicating a Grave

Frank, thanks for the great question. I had to go review conference talks and other resources to learn more. I reviewed the official documentation from the Church on performing any priesthood ordinance. This is part of the introductory paragraph:
“Priesthood ordinances are sacred acts given by the Lord and performed by the authority of the priesthood. Priesthood blessings are given by the authority of the priesthood for healing, comfort, and encouragement. Brethren who perform ordinances and blessings should prepare themselves by living according to gospel principles and striving to be guided by the Holy Spirit.”

I then looked at the introduction to dedicating a grave and found this: “A person who dedicates a grave must hold the Melchizedek Priesthood and must be authorized by the priesthood officer who conducts the service.”

The following is my opinion. Of all the priesthood ordinances the dedication of the grave and the blessing of children are the least obvious of any of the ordinances. I do not understand why the Lord has given us priesthood ordinances that have no apparent connection with one’s immediate salvation or well being. But time and time again the Brethren mention that we gather in meetings and perform ordinances with the aim to give comfort to those who suffer. These ordinances are given to us from the Prince of Peace. He has promised that He will give us His peace and that His peace is unlike anything the world can give us. I believe these ordinances are given to us to provide comfort and Spiritual reassurance in times of worry. (As to the blessing of children, it used to be relatively common for children to die before their first birthday. Parents were always worried as to whether or not any one child would make it to that all important first birthday.)

I hope this helps. To answer your one question directly, no, it is not necessary for the deceased. They are beyond the reach of mortality by that time. These ordinances are for the living.