My dad's a consultant in the insurance industry. He says the job description is in the title. It's mostly conning and insulting people.
People will have a business doing 50 mil a year and hire Deloitte to implement their ERP. No shit you're going to get Deloitte's D team. You have to pick a consulting agency that aligns with your business size.
I generally find them useful if you know how to use them. A lot of people are dumb as f*** and think hiring them solves all their problems. You know your shit and just need extra hands? Consultants.
You want someone to deliver you an end to end software solution and ALSO build all your business practices? Yeah doesn't f***ing exist.
My best analogy would be you hiring day laborers to work at the railyard and then ask them how you should run the yard. Thats why consultants get a bad name.