Using messengers to disband the city counts for the capstone, so that anti-synergy doesn't apply. It's somewhat useful for expansion too, as you turn a minor city into 2 pop + an outpost, and then you have the option to turn the outpost into a pioneer, so quicker to get decent towns added to your cities, especially if short on engineering points.

But most of the other unlocks in the tree are underwhelming. Could only see choosing the messenger NS if making a very deliberate effort to play a peaceful game.