Audio Priority Normal or Boost?

In the Device Setup you´ll find this Audio Priority setting. What does it actually do? I´ve never really figured it out.

I have projects that are all MIDI tracks. Then I have projects with only one MIDI track and lots of audio tracks. Which setting I should use on which projects and should I switch back and forth between this Normal and Boost setting depending which project I´m working on?

On the dialogue where you would select this option is a context sensitive help that describes it pretty well.

The “Help” button is disabled (greyed) for this screen…