It means that that change will not be to everyone's advantage, since some people might suffer from it. If for instance books are not printed any more but only read online, some categories of people such as typographs and booksellers of physical books will risk to lose their job.

It means that it will not help everyone. It will hurt some people. An "advantage" is something that helps you win against other people. In basketball, height is an advantage. Something is "to your advantage" if it gives you an advantage. "In preparing for the TOEFL, it will be to your advantage to find a study guide with actual practice questions." "In giving a talk, it is to your advantage to arrive early and see how the room is set up." "Automation is to the advantage of manufacturers, who lower their costs of production; it is to the advantage of consumers, who get manufactured goods at a lower cost; but it is but it is not to everyone's advantage, because it results in workers losing their jobs."