@lunarood Favouriting a post to me is a way to say "hey, I liked this post" both to the autheur and the onlookers. Boosting is something I do if I specifically want my followers to see a post, for example if I would like to give reach to an unanswered question or show off someone else's cool project or funny joke.

For a real-life meatspace analogy, favouriting a post is what I do when I chuckle at my phone, boosting is what I do in lieu of turning around my phone to show it to my girlfriend.