Pareto optimality, roughly, describes a situation in which no one’s position can be improved without making someone else’s position worse. That definition comes from Stephen H. Kellert, Borrowed Knowledge: Chaos Theory and the Challenge of Learning Across Disciplines (Univ. Chic. 2008) at 161. If you contemplate a change in your guidelines for outside counsel, you have not reached Pareto optimality (theoretically) if no incumbent firm comes out worse off and some firms benefit.
A blunt rejoinder could be that this is nonsense, because the benefits and detriments to firms don’t dictate what a law department does. A practical objection would be that you can’t possibly figure all this out. Still, Pareto optimality describes a concept that has some force: you are in the best situation you can achieve (theoretically) if a change to help someone hurts someone else.
This view takes a very positivistic stance, that everything is measureable, almost utilitarian. It excludes some important values, like justice and equality, while giving more than full measure to technical analysis.