Think of Personas as different ways of working within Affinity Photo. If you want to work on a particular facet of photo editing (e.g., retouching) jump to that Persona, then once finished, switch to another. Each Persona is equipped with its own tailored set of tools.
The idea behind Personas is that the user interface is kept uncluttered, thus improving your workflow and general ease of use. This ensures maximum efficiency and design focus.
Here's an overview of the set of Personas available to you:
When you switch to a different Persona, you get a different set of tools for specific photo-editing needs.