The Buddy Adventure update for Pokémon GO enhanced the buddy system. Your buddy can now appear on the map with you, level up, go exploring with you, and even help in Pokémon battles. The updated also introduced a new item called Poffins.
The in-game description of the item is “Feed this special treat to your buddy, and it’ll happily join you on the map for an extended duration.” Normally, you would feed your buddy a Berry to get them to join you on the map, but if you wish, you can feed them a Poffin instead. Poffins will act the same way three Berries would. Poffins also cost 100 Gold, while Berries can be found by spinning Poké Stops, or from gifts sent between friends.
The Poffin will have other effects on your Pokémon, however. As you can see in the image above, not only will the Poffin bring your “give your buddy a treat” hearts to full, it will also double the hearts you can potentially earn. Typically you can only receive ten hearts a day. Hearts of the measure of your buddy’s affection for you, and the more you earn, the faster your buddy will level up. After giving Machoke a Poffin, you can see that the hearts you can earn will double, allowing you to level the buddy faster than usual.
If you do plan on using a Poffin, it is a good idea to use it on a day where you will be able to play a lot of Pokémon GO, and take full advantage by earning the full twenty hearts in one day.