I suppose it also depends on the application. Std motor can tolerate somewhat looser springs ok, you need more stiffness to help prevent axle tramp with a higher output engine (or use traction bars).

Then it's about ride height and whether it's for drag racing or circuit or what. flipping spring eyes to get it lower will affect launch a fair bit as it has hte axle centreline higher than the front spring pivot point, so it sort of unloads the rears at launch. for a dedicated drag racer, you'd want the opposite, so it would push the tyres down and try and lift the rear of the car up on launch, adding yet more downforce. It might not actually lift the rear, just the directions the forces would be going in.