A consultative approach is a process of discovery and proposing solutions. The discovery and the solutions are based upon knowledge about the client's business. The sales delivery approach works well where deliverables are well defined and very little customization is required. The consultative approach works well in environments that are not yet well defined, or do not lend themselves well to standardized solutions. Too much hubris and not enough wisdom.
Consultants are most often specialists.
Socrates was declared the wisest man in all of Athens by the Delphi oracle because he knew what he did not know. Skeptical, Socrates set out to test the oracle by questioning experts in the community. He found that although the city's best minds were experts in their fields, they all made the mistake of talking as if they were just as knowledgeable outside their areas of expertise. The city's experts allowed themselves to be susceptible to hubris. Competence and wisdom are not synonymous.