Question about the way pros harvest animals

So occasionally I watch youtube videos of pro players and they do something with animals that I do not understand. So as far as I know, animal food(sheep, lama, turkey etc) naturally decay over time and the best way to minimize decay is to put many vills on the animal to harvest it quickly. So I usually kill only one animal at a time and then put 6 vills or so on it, moving on to the next animal once it's fully harvested. But I've seen high level players put 3 vils on a sheep, and 3 on another sheep..and I don't understand why they'd want to do this? They do the same thing with boars too, like putting 5 vils on a boar and 4 vils on a sheep etc.