In terms of the pricing options, what is going on here is that we are providing more control to authors:
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Before: "Minimum Price"
After: "Allow Free Purchases + Minimum Paid Price"
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Obviously, the Before is simpler, since you just pick one number.
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However, that prevents you from doing the following:
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1. Allowing free purchases

2. Having a higher than $7.99 minimum paid price
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In terms of why #2 is useful, it's in the case where a membership is required for free purchases.
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The use case is an author who wants their book to be free with membership, but the minimum paid price is, say, $20.
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Before that was not possible. Now it is.
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We can obviously do things with the UI to make things seem simpler (such as hiding the full set of choices behind some advanced settings thing etc.), but the main point is that it is more complex now because what was one choice is now two choices :)
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(Note: When a reader membership is not required for a free purchase, then being able to choose the minimum paid price is not as important, obviously. But some authors may want it, so we don't remove the capability.)