Why the consulting firm is better for engineers?

How it can be better?  Assuming the engineer already have sufficient expertise and experience, being in a consulting firm may be better for the engineer as there ought to more exposure to engineering issues as there would be projects from multiple clients.  Therefore, the engineer should not become a desktop consultant and try to gain even more experience from the different challenges that the engineer must face.

No way .. Engineers are the beings of site and consultants are only living in Documents. who has very good experience from site only can become a good consultant.