Do not be confused. It positively makes no difference, but only if you set Render Quality to Final Render at Render tab.
You may then have the viewport set to Medium, Quick or Minimal. The moment you hit Export, the scene viewport is automatically switched to High, scene rendered and then vewport is switched back to the initial mode.
If you however leave export settings at Preview mode within Render tab, the images would be rendered with the current quality for the viewport (High, Medium, Quick, Minimal, or Custom).