Consulting is a business.
I was a consultant for a while and there was a good reason why it made sense for me to be one, just as there was a good reason why it made sense for my customers to hire me as a consultant versus hiring me as a full-time employee.
In the specific situation that AMD is in, the consultant is getting paid to be the bad cop to internal managements good cop persona. Internal management has no choice but to let people go, even the good people, because they have a cash crunch coming and they must take drastic action to avoid catastrophe.
But internal management also has to retain confidence in the eyes and minds of the employees that aren't being let go. It is morale triage, attempting to keep the absolute worse from happening.
Consultants in this situation provide two benefits - limited liability (reduces claims of biased or prejudicial layoff selections) and filling in the role of the bad cop.
Just look at the response within this thread to the very concept of an external consultant being involved in providing guidance for the layoffs. People love to hate, and they just need a sacrificial lamb to vent that rage towards.
Downsizing consultants willingly let themselves become the scapegoats so that management can avoid taking that blunt force full salvo of anger and hurt from the employees that don't get let go - management needs them to still take direction and rally themselves to come in to work and actually get the work done.
The charade of the downsizing consultant fulfills the morale triage that is needed internally with employees, and the association of making downsizing decisions on the basis of external benchmarking and guidance provided by consultants fulfills the morale triage that is needed externally with shareholders and creditors who also need to have confidence that management is doing what it is doing because it needs to and not because it has no idea what it is doing.