The proliferation of job titles in an organization encourages the diffusion of responsibility and dilution of vision.

Panchal's Directive provides a guide to the number of different titles in an organization:

Take the square root of the number of people in the organization, then divide by two. 

Four people? One title.  Twenty-five? Around two or three. And 100 people means about five titles.

A typical Scrum team of nine people?

Well, you get 1.5 titles, which probably matches reasonably well the delivery team and product definition roles.

You'll notice that this rule doesn't scale to very big organizations, but then again, nothing does.

ps: Thanks to Michael J Tardiff, my colleague for his valuable contributions