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Ime it's like operating systems, most people you hear seem overly opinionated when it's not that big a deal.
We have a non-flappy paddle DSG. So a quick way to lower gearing is Sport mode, if you need real control you push the stick to Manual then push up or down. I found it really useful when staying with a mate in darkest Devon down a long steep rough road. The auto jumps to 2nd almost immediately (which was too high) so used manual a lot to select 1st. I do also use it for fun sometimes.
But really, it's good for either long or steep or both hills, but as far as I'm aware most autos let you select a lower gear so you can avoid over heating the brakes and because if you're braking down a hill unnecessarily you're just turning your fuel to heat and leaving the car in gear down a hill drives the engine without needing fuel and out of gear you're essentially idling so using fueland not in full control. I've only driven an auto a few times and found it a bit confusing at first, changing gear manually doesn't really involve thinking, even if I've not driven in months, kinda muscle memory.