To assist players with their hit chance, Karmic Dice is designed “to bend RNG in the rolling character’s favour” for those attack rolls, saving throws, and dialogue roll moments. One thing to note about this design is that it also applies to NPCs and enemies, which means they can also land those critical hits on you during combat for additional damage.
I think it's to stop a bunch of "misses" from happening to you, but it helps enemies too.
I'm not sure if what I played through EA with was Karmic Dice or the weighted option from before, but personally it felt like it actually stacked things against me. I had built for fairly high AC but found that I was still getting hit a ton, and since my AC requires such higher hit rolls, I was getting crit a ton. Once I tried another playthrough with the option turned off, rolls suddenly felt a lot fairer and weren't punishing me for making a tanky character
I am thinking the only reason I might turn it on is when having to reload a saved game for multiple failed dialogue attempts or something like needing a 20 to unlock something and I keep failing. Otherwise, for combat, doubt it is worth it.