I was under the impression that it allows you to cast at higher power without fizzle. From my experience it 'kind of' seems to do that but only for offensive spells.
When my hybrid classes have begun to cast, I was surprised they had a very low magical skills, but casts always successful. Then I suggested that in magic skills there is a bug. In all normal mechanics, a skill is needed to learn the spell, its action is discrete, and there are no questions. Here is my alchemist (thaumaturge), and only he, sometimes fizzle spells, But it's his skill alchemy = 80. At the moment it seems to me that the failure of the spell occurs when an unsuccessful test of intelligence (but I do not have 100% confidence).
By the way, did anyone notice any changes in any prices when changing the "barter" skill? I changed it directly in front of the store, but the prices remained the same.
At the moment, I have a claim to the skills of all magical schools, the skill "music", "barter", "metalsmith" and "stealth" ("stealth" works, but for some reason does not grow, like "music"). In addition, I did not check the "nature lore", "ansient lore", "diplomaty" and "mephistics". Berserk under the skill "berserk" always beats party members (low skill, maybe). All other work OK.
In general, the game brings strange feelings. I have not been playing it for three days, because I understand that some of the mechanics do not work, but at the same time I feel like a drug addict who has been deprived of heroin.