Dad worked at a bank (just below CEO). He once said that McKinsey was most useful when you wanted to kill a project diplomatically, and make sure it would stay put. Have McKinsey come in, make the recommendation that X project was no good, and kiss it goodbye with McKinsey absorbing the blame. Other way around was to give projects some extra push and credibility.
We came up with a product internally. So our CEO hired a top-tier consulting company to sell our own idea back to us. That process cost millions.
But they do make real slick presentations and they have higher status than internal staff, and the CEO can say that a top-tier consulting firm recommended we do x, y and z... Blame insurance is right.
Once you hit a certain scale, e.g. where CEO is so stratospherically above rank-and-file in social status that it's not appropriate to speak directly anymore, consultants can act as a social buffer. Among other things they can launder recommendations from regular staff to management and put that objective shine on them.
The downside is that we know for a fact (when they accidentally published an android app to the playstore, I reversed it and it was our code) that collateral, research and demos that we paid for got sold to others.
Everyone should watch the series House of Lies, that completely supports this description ;-) It's the most enjoyable and subversive show about the world of business ever.
I guess the main thing I missed in my pithy assessment was the way they'll update you on "industry best practices" (=your competitor's processes that are working better than yours). So they're also a kind of mix of corporate spies and governance R&D mutual aid program.
actual mckinsey employee. no, other posters don't know what they're talking about. Fees will vary, but that's way, way too high except for perhaps the senior partners (who wouldn't be there most of the time anyway). ffs