Inside McKinsey 15 years ago
Well, a big share of the work I was involved in as a management consultant resulted in clear measurable $$$ to the client. Typically in the range of 5-10x the fee. One of the teams delivered something like 20x the fee in a project for the government.
And yes, that means that the client who payed 2 million USD to run a team actually got 40 million USD in payoff from this. This is of course an outlier, but it is still true. I have seen the details of this project myself (as it was a public engagement).
Why hasn't anyone heard of this? Because the glory of the successful projects are always given to the client executives/team.