First of all because those fillings that do not
close can not guarantee the safety of teeth underneath. Secondly
if the masticatory surface has been completed similar to the
natural surface, it also favors the masticatory system (it is
easier to chew food with the well indentured filling surface).
White fillings are harder to make. But using proper
chemical technique it will merge better with the tooth and will
be amazingly durable.