1. I like my bat length to be a size-6 bat (which I hold from the top of the handle). A rolled-up second grip, marks the spot where the SH bat length is size-6.
2. For my top hand, left, I like the handle to be thicker than the bottom. A rolled-up second grip for the top half of the handle achieve that for me. For my bottom hand (near the neck of the bat), right, I just pinch the handle so I prefer it to be thinner than the top part.
3. This setup, adds bat speed for bats that are bottom heavy and have a mid-low sweet spot. Any bat, like Amplus, which has a high sweet, this setup affects my timing. So, I don't use the rolled-up second grip for my high middle bats.