Fast-forward 10 years, and now you're a pretty big company. You want to start manufacturing your product yourself instead of sending that work out to someone else. Do you know anything about managing a manufacturing operation? Say you want to acquire a company. Do you know anything about integrating it?
I think it provides some value, but I am not a huge fan. In my experience, the devil is in the details and the failures come during the implementation, and the management consultancies in the Marvin Bower tradition explicitly side-step implementation.
That is also a practical reason why consulting firms hire from Harvard and care about SAT scores. Getting a 1600 SAT doesn't mean you're a good manager. It's probably a good indication you're good applying abstractions to concrete situations.
Most big management consulting firms these days also do both management consulting and system integration. The margin on management consulting work is sick, but the projects aren't that big (a few million dollars over a couple months). The margin on implementation projects is much lower, but the projects themselves can be enormous (think hundreds of millions over several years). So you're fucking your implementation guys if you deliver an unimplementable plan. And in a partnership model, if the implementation project fails, the partner who did the management consulting piece of the work still takes a hit.
Other times tough choices need to be made, and it's easier to fire 10K people with a powerpoint deck from a reputable firm.
Management consultants often get called in to vet risky projects management is considering. The idea is that if a trusted outsider OKed the project, and it fails, then management at least didn't act irresponsibly in undertaking it. There's a surprising amount of ass-covering in this world.
The other scenario is when a decision needs to be made that will inevitably hurt someone in the company, so it's hard to find an impartial insider. This is why management consultants get pulled in for re-orgs, for example.
You might be thinking of strategy consultants, which are a rapidly-disappearing subset of management consultants. They often deal with very high-level problems such as "our company's market position is disappearing; what adjacent markets can we move into?" You then get an answer that may not be the one you were looking for, such as "you should look to sell the company while your value is high". But this is often backed up with a dizzying amount of thorough analysis, so it's not just some random guy telling you something.
Much of what I've been doing recently has been helping development organizations at large companies convert to "modern" management practices. Things like bringing your ops folks into the dev team as DevOps, how to structure teams to manage automated testing, planning how dev environments (i.e. CI environments) should be structured and used so that continuous delivery is an option down the road, etc.
I happen to focus on software development and technical operations because that's my background, but there are people doing this for manufacturing, shipping, call centers, etc. There is sort of an "ideal way" (aka "best practices") for most companies to do most things. HN might cry "No there's not!" but this is actually true because most of our clients are too big to really be innovative. It can be hard for an insider to see what's working and what isn't. Also, because I move from client to client relatively often, I get to see how a lot of different companies do things, so I can bring perspective that someone who only works at one company all the time can't.
And usually, it doesn't matter if the manager trusts my opinion or not. Either myself or someone else from my firm has developed a trust relationship with someone higher up in the company (usually a VP who has a discretionary project budget) who has brought us in to help. The core of the business is trust: that's why you have to be a likable person capable of building lasting human relationships. It's in both parties' interests to maintain these relationships; the consultant uses them to sell work, and the client uses them to solve problems. It's a win-win.