This would push users toward local posts (especially on smaller instances) while still supporting a better distribution of user engagement over the threadiverse. And if you don’t trust that it was implemented correctly – you can simply check it by counting the amounts of posts against your chosen probabilities.
Edit: changed feed name to mixed-feed
It modifies the feed according to your sorting option, which uses different algorithms.
You can read more about here: https://join-lemmy.org/docs/users/03-votes-and-ranking.html