Prestige and the perception of impartiality, alongside the ability to serve as fall guys. And to a significantly lesser degree they can tell you things you actually don’t know or make recommendations when you’re stuck because they’re an outside set of eyes.

What this means is when you decide to make a controversial decision they can take the heat in place of experts, and unlike internal experts you don’t wind up in a particularly flimsy situation when you inform them of what they’ll be suggesting. And if it all goes as poorly as it might you can blame them. (And everyone knows this so the consultants are shielded)

And for the situation where you don’t actually know what to do, theoretically thet may or may not be bad at it. If you’re stuck you’re stuck and not only can they possibly help, they can definitely provide cover for a bad call or an unwinnable situation

To a certain degree they’re a result of people in a position to spend large amounts of money whose job is to make calls.