THEY ALSO GIVE YOU VALUABLE LOOT TO MAKE STUFF. RESIN, SKINS, WOOD, ROCKS.
They are very easy to kill if you use just a knife, the knock back from the knife prevents them attacking and energy is bare minimum using a knife. You can repeat knife attacks quicker than any other weapon.
also you get much needed experience to make your skills way better so they are essential to the game.
I used to only use a bow and arrows which was so slow and used up to much energy.
also the atgier is a must for wiping out hordes so use your head, no enemies means no more skill increase.
Later on you can use the troll to knock down valuable wood for your buildings arrows etc.
Also the trolls will fight other enemies for you , well not for you ,but they do it so just get them near each other.
Also you can run around and destroy the spawn spots eg the pink smoke from the ahh what do you call them