Dying repeatedly in Sekiro infects characters you've met with a mysterious illness called Dragonrot. You can cure every character's dragonrot at once with a Recovery Charm. Veteran restorer of cut content, Lance McDonald, has discovered that the system didn't always work this way. Using patches to restore lost code, McDonald finds Dragonrot Pellets that let you restore characters' dragonrot one by one.
This method for curing Dragonrot was cut at some point during development, but restoring it unlocks new dialogue exchanges throughout the game. Dogen in particular has more to say. New dialogue options open up when you offer him the pellets, and he even talks a little bit about Emma.
The new dialogue doesn't dramatically alter Sekiro's story, but every scrap of dialogue is useful for lore-hunters. Plus, who knows what other cut content can be restored as players dig into the game's code. McDonald has previously found entire bosses and cut multiplayer features in Dark Souls and Bloodborne. McDonald's investigations are supported by a Patreon.
The extra dialogue is neat, but it would have been arduous to run around giving every NPC a pellet to keep them healthy. In addition to restoring cut dialogue, modders have been busy with Sekiro. They've added a photo mode and a costume pack that lets you play as various NPCs.