I want to promote my website.
The SEO all-rounder can do everything, of course, but time is finite and some projects are absolutely massive. They’ll need help, and will probably need to work with other teams. Delegation may come into play, even if they can do it all.
In bigger companies (and agencyland) you often find specific people doing specific SEO tasks. Some projects are vast and take an age to complete, as anybody who has experience of a site migration with gazillions of web pages will tell you.
Broadly speaking, I think there are three areas of focus – technical, analytical, and creative. There is a great deal of overlap in a lot of specialist roles, whereas others are more skewed towards one or two of these areas.