Think of Personas as different workspaces within your application. For vector design work you can use the default Designer Persona; for additional pixel brushwork and pixel selections, the Pixel Persona is the choice for you. One final Persona, Export Persona, is ideal for exporting specific areas of your design as usable graphics (for web, print, etc.).
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 design needs, e.g. for vector drawing, raster painting and exporting.