What are the benefits of having both digital and physical collections management duties handled by one position or person rather than separating them into distinct responsibilities? I'm specifically interested in benefits to the organization beyond personnel cost savings.
The benefit that most stands out to me is that this type of organizational methodology emphasizes the similarities between traditional (physical) and digital collections management.
So often in digital librarianship, folks tend to act like they have forgotten everything they know about (for example) how to manage collections when the content is digital. But nearly all the same rules and best practices will apply to digital vs. physical collections. Obviously, there are exceptions. But my point is that the sooner we stop talking about traditional vs. digital librarianship, and just focus on big-L Librarianship, the better we will be.
Related thought: it may be tempting to assign digital library tasks/duties to a tech-savvy employee even though they may be lacking in library skills. This can be a mistake, as it is often the case that a good librarian can learn enough of the technology to do her job. But the opposite is seldom true. It is usually much harder to teach a non-librarian techie the skills necessary to do an equally-good job. The domain knowledge of librarianship required to do the job nearly always outweighs the needed technical abilities.
Digital is just another format. If you must divide collection responsibilities across more than one position, it makes more sense to divide it by interest area rather than format. If you divide by format, the digital person has to have the same knowledge about upcoming publishing releases, awards, etc as the physical collection manager - two people are studying the same publishing journals.
Dividing by content area (adult vs children's, fiction vs nonfiction, science vs liberal arts, etc) allows for subject specialization which will contribute to a stronger collection. If one person is ordering all the adult fiction, for example, they will make sure they have new titles in the formats that are most likely to be used, and if a title is unavailable in digital, they will know to order more in other formats.