Some mods fill obvious gaps. Others, you don't know you need until you discover they exist. For instance, I had no idea I needed a mod that gave me a randomized psychedelic experience every time I drank skooma until I learned it existed, and now it's an essential part of every playthrough.
The Dragonborn's Bestiary is in the same category. It's a mod that adds a new menu you bring up by pressing K, which keeps track of every creature you've encountered. Kill your first mudcrab or skeever and a pop-up appears telling you that you've unlocked the relevant entry, which contains info on what kind of loot they're likely to drop and any resistances or weaknesses they have.
Killing creatures isn't the only way to add them to the bestiary, however. You won't need to murder a dog just to complete your Skyrim Pokédex. Interacting with pets adds them to the bestiary, and you can also fill it out by summoning certain creatures, transforming into them, or reading books about them.
