It doesn't necessarily "add the artist", but it helps them to see what you like and suggests different curated playlists and albums that they think you might enjoy in the For You section. It's just a more "on the go" version of what they make you do when you first set Apple Music up (all the bubbles). If you heart a lot of jazz, they'll have more jazz-orientated playlists and album suggestions for you.
It doesn't necessarily "add the artist", but it helps them to see what you like and suggests different curated playlists and albums that they think you might enjoy in the For You section. It's just a more "on the go" version of what they make you do when you first set Apple Music up (all the bubbles). If you heart a lot of jazz, they'll have more jazz-orientated playlists and album suggestions for you.