I have found it useful for driving in hill country (to avoid having to ride the brakes downhill) but beyond that I'm not sure there's much practical benefit. I used to think you could downshift to buy you more time to coast to a stop without having to touch the brake and save some gas, but I think even using the brakes is enough to get a modern car to cutoff fuel flow.

I sometimes use it in town because modern automatics want to upshift very aggresively to maximize fuel economy. That means the engine is almost lugging most of the time, which isn't really good for it. So I'll use the manual mode to keep the car in a gear that results in a slightly higher engine RPM.

It's not like a real manual though, there's no tactile feedback to changing gears or knowing what gear you're in by the position of the shifter, so I don't use it all the time.

If you're getting into motorcycling, it's not a bad way to start practicing with it since the electronic override is often like most motorcycle's sequential gear shift.

I use it exclusively to downshift when I need more power, quickly. It allows me to drive in ECO mode to save gas, while avoiding sluggish downshifts by doing it manually.

I assume those are there only for fun. Not much different than driving a manual transmission these days.

Useful if you need to tow a trailer. Otherwise it's just a novelty.