I set centre shot then adjust to either move the arrow impact left or right.
Or as I imagine it,,,adjust for dynamic spine.
I've never used anything other than the medium pressure spring and I've long shot 40-50 lb @27.5" on my target bows.
If I couldn't tune with the medium spring at those weights there would be something seriously wrong with my whole set up, and spring adjustment would not fix it.
John.