You'll notice that on the right side of the screen underneath the big green Continue button, it says Major League Baseball. That dropdown allows you to choose any of your minor leagues (you may already know this). At any rate, my best guess is that on this MLB panel you can choose to select to base on Current Ratings or Potential Ratings for minor league depth charts & pitching staffs
universally - IOW, for your whole baseball system - or you can defer this selection to whatever you have selected for each minor league.
So if, for example, you wanted lineups & pitching staffs for your all of your minors leagues to be determined by Current Ratings, you'd select that here, on the MLB panel you've attached. However, if you wanted your three AAA leagues to be on Current Ratings, some of your AA leagues to be on Current & some on Potential Ratings, and your A and Rookie leagues to be all based on Potential, you'd select Use Minor League Settings here, and then would go to this panel for each minor league and select Current or Potential, as desired.
That's my best guess & hopefully this makes sense
And I'm also guessing that this section of the manual hasn't been updated. It could be that this is a new feature for v25, and the most recent manual is for v24...