:???: Uh, that's still only two ranges, just lower.
No, it's three. If the cases have different ratios, it gives you three options.
Say the front case has 2.72:1 and the rear has 4:1
With just the front case in Low, you have 2.72:1(2.72 x 1)
With the front case in HI and the rear in Low, you have 4:1(4 x 1)
With both in Low, you have 10.88:1(2.72 x 4)