It serves as a third party objective rule by which to understand the world. Whether we agree with it isn't really the point, the point is that it exists independently of human experience and emotion. I think you may be missing the meta-point here of objectivity - it by its nature does not care about these things.What role does objective morality serve if you are neither going to act in accordance to it nor support those who do?
In day to day life almost no-one lives by objective standards and everyone who does will at some point break them unless he's a literal saint or angel. Objective morals often serve as a benchmark, an ideal, rather than what people actually believe or do. Ideally, most people believe in stopping animal suffering - in the real world we use all kinds of products from animal suffering and really don't care.
Often we don't support those who do because of the problem of people being too good. Studies have confirmed this - when one person in a group exhibits highly moral behaviour, he is hated because everyone else realises they are not living up to the same standards and it then reflects badly on them. Everyone prefers to live in an average society where sin and righteousness appear to be in some kind of balance, otherwise we hold people to either incredibly low or unrealistically high standards.
Yet in order to have standards at all we need an outside source, an objective source, even if we routinely ignore it.