What does loving a playlist (not a song/album) do? In iTunes (in Windows), it is possible to right-click a music playlist and select "Love". What does this do? What effect does it have? (Thankfully, it doesn't mark all the tracks in the playlist as Loved.)
Source

The For You section of Apple Music, in the Music app on your iPhone, iPad, or iPod touch, in iTunes on your Mac or PC, or in the Apple Music app on your Android phone, is where you'll find suggestions from our experts who know and love music. Our recommendations are influenced by:


The music that you listen to from the Apple Music catalog.
What you tell us you love or dislike.
The genre and artist choices that you made when you first joined Apple Music.


Tell us what you love or dislike

When you listen to songs and albums, you can let us know if you love or dislike something. We use this information to give you better suggestions.


On your iPhone, iPad, or iPod touch: While listening to a song, tap the player at the bottom of the screen to open the Now Playing screen. Tap , then choose Love or Dislike.


Update your choices

When you first join Apple Music on your iOS device or computer or your Android phone, we ask you to choose genres and artists that you like. At any time, you can change these initial choices.   

On your iPhone, iPad, or iPod touch


Open the Music app and tap For You.
In the upper-right corner, tap Apple Music profile icon  or your photo. 
Scroll to the bottom of the page and tap View Account, then tap Choose Artists For You.
If you want to reset your choices completely, tap Reset. If you want to change or add to the choices you made previously, follow the instructions to like, love, and remove genres and artists based on how important they are to you. You can also search for specific artists and genres.
When you're done making changes, tap Done.


On your Mac or PC


Open iTunes.
If you’re not signed in, sign in with your Apple ID.
From the menu bar at the top of your computer screen or at the top of the iTunes window, choose Account &gt; Choose Artists For You.
If you want to reset your choices completely, click Reset. If you want to change or add to the choices you made previously, follow the instructions to like, love, and remove genres and artists based on how important they are to you. You can also search for specific artists and genres.
When you're done making changes, click Done.