A quote from Reinventing Organizations, about roles, job descriptions and job titles in Chapter 2.2: Self-management (structures), page 90:

[In] Teal Organizations […] people are not made to fit pre-defined jobs; their job emerge from a multitude of roles and responsibilities they pick up based on their interests, talents, and the needs of the organization.

• Frederic Laloux, Reinventing Organizations

In my opinion, this is the role of the software consultant when working with a client: even if the customer has asked for help in some parts of their activity, a senior-enough consultant can discover other areas where they can add value, even if that new work doesn’t have much in common with the initial request (this change should be approved by the people that will be affected).

This is also a thought that Mash and Sandro were discussing lately.