I've seen it where a project needs to get done but the company can't hire anyone for it due to firm wide hiring freezes. So in come the consultants to bang out a sloppy version 1. In the meantime you wait it out until you can hire a real team and gradually transition them in to rewrite what the consultants did. At least the company will have learned something from the consultants trying to implement the project. When your domain is complicated and has many dependencies there's some value in having anyone trying to figure that stuff out.

Of course, when the project is inevitably a late, half functioning, buggy mess you get to blame the consultants.