LilliThem: Faving posts on Mastodon is useless, only the OP sees it.
Me, when a post gets faved: awwww, little internet hug ✨
Andi@Lilliana_S actually favoriting a post means more people see the original post on the local server, and across the network: 👍🏼
Falcon@Lilliana_S @theandil no
Even the picture you shared doesn’t mention anything about favoriting, only boosting
Favoriting maybe will put the post higher on the part of the explore/search area of the app, but that’s it
Jane Dunlop
Rev.Hans 
@hanspetermeyer @janedunlop @Lilliana_S @theandil
boost = retweet
So you are sharing that to your followers
Favorite here just adds a star to it and let the person know their post was starred. It does NOT does like twitter where it could should to your followers that you liked it. And it's also not going to affect your timeline, showing a "Because you liked XYZ...: