Expedited Birth Certificate California
A birth certificate copy is still an official document, printed on official paper, and can be identified as a proper document. A photocopy is not necessarily accepted by any or all government entities, and in most cases will be refused. In today's world, it's increasingly hard to do anything that is government run without your identification papers.
It is better to have a birth certificate copy, because this copy can be more easily replaced in the event of a loss. If for some reason a child needs their certificate to enroll in some type of youth sports, it is easier to breathe knowing that a copy is more easily obtained than an irreplaceable original.