Comment by gaius

The thing is, on an individual level, consultants really do work like sled dogs. If you have something in mind that needs a dozen fairly smart people to go to North Dakota and work 90 hrs a week for 3 months, consultants can do that and your regular employees probably can't (or won't).

However it's up to you to actually have something like that in mind in the first place... I can't think of anything offhand myself!