While Apple likes to put emphasis on the human curation that goes behind the scenes, Apple Music is still largely powered by algorithms that learn about your music tastes by looking at your own library, but also by looking at your recent activity, including the songs you Love.
The more you play a song, the more the algorithm understands you like that song, and maybe by extension that band. If you Love a song, you're also signaling that this is a tune you particularly enjoy. Algorithms then crunch data based on your behavior to improve music suggestions for you.
For the past year, my favorite way to train Apple Music's algorithms was to actively Love songs. It was a quick and simple way for me to tell Apple "hey, I really like that, please play this more often and also play more songs similar to that one."
But the big, bold, confusing mess of a redesign that happened with iOS 10 has changed a lot of things, including how you now Love songs on Apple Music.