...a favorite is for the author ("I liked this thing you shared")
...a bookmark is for you ("I want to see this again later")
...a boost is for your followers ("more people should see this")
Public likes are toxic and add very little value. Because of the friendship paradox (https://en.wikipedia.org/wiki/Friendship_paradox) your followers will have more followers than you on average, and their posts will receive more likes than yours, which leads to you feeling less appreciated.
Personal Mastodon instance of Beto Dealmeida