On road I don't see the point, any decent derailleur works well in all conditions you regularly experience. Generally rides (consciously or not) let up on the

On road I don't see the point, any decent derailleur works well in all conditions you regularly experience. Generally rides (consciously or not) let up on the torque to improve shifting, not a big deal. However on a MTB it's more challenging, more forces (sideways, skidding, jumps, rock gardens, etc), larger temperature changes, more variable torque (large gear ranges and suspension travel induced torque), and more need for shifting under full torque. For example when climbing a steep technical climb strewn with rocks and roots. All cassettes in the last few decades have on/off ramps to help shifting, however it's pretty much the luck of the draw when you shift, doubly so when shifting multiple gears at once. SRAM has managed quite the evolution and got the bike industry on board. First they replaced the weakest part of the frame (I've personally lost a frame to this), the derailleur hanger. Now the derailleur is effectively attacked to the rear hub and is perfectly aligned, there's all kinds of silly demos showing them being hit by hammers or standing on them when the bike is on it's side. I saw a study showing that on 5 year old bikes something approximately 50% of bikes has a misaligned hanger, enough to make shifting worse. Now with that crazy big improvement in strength, durability, alignment, and best of all the bike industry now doesn't require a custom hanger for every bike with variable derailleur positioning, it can now just design in the bike axle. Now they have a electronic shifter that gets rid of temp variability, cable issues, and can tuck in to avoid hits. It also knows where the ramps are, so it can shift exactly when needed, which allows full torque shifting seemlessly. In fact people complain it doesn't work particularly well when on a bike stand, but does extremely well when actually ridden on the trail. Is it worth the cost, complexity, and charging once a month? That's up to the end user, but it is a pretty noticeable improvement. Some ebikes can supply the derailleur from the main battery. I'm pretty late to the game with most bike developments, but I'm considering this one, perfect shifting under load is pretty attractive. My current bike is pretty finicky shifting wise. I replace the cable, casing, and clean/lubricate my derailleur and it gets better, not great though or at least not for long.