Alchemy is one of multiple crafting systems that you'll use in Kingdom Come: Deliverance 2. You'll need to use alchemy to complete some quests, but it's generally useful throughout the game due to the potions you're able to craft with it.

In the Finger of God quest in Kingdom Come Deliverance 2, Henry makes new friends out of old enemies, and helps to treat the sick and wounded around camp.

Belladonna is an essential alchemy ingredient in Kingdom Come Deliverance 2, letting you brew Saviour Schnapps

Depending on how you approach the quest, “For Whom the Bell Tolls,” in Kingdom Come: Deliverance 2, you might need to craft a Digestive Potion. If you were able to pass the skill checks with the chamberlain in the noble's kitchen and convince him to let you brew him a Digestive Potion to help with his stomach problems,