When, as game designers, we give an NPC Rooting Interest, the player will, as if using Tolkien's "Stones of Seeing," we look at the world through that character's eyes and experience that NPCs emotions.
It becomes even more of an Emotioneering tool when you start having the player experiencing the emotions of numerous different characters simultaneously.
How many characters did you identify with in Star Wars Episode IV? How many in The Matrix? How many in the Lord of the Rings films? It's no wonder these films take up permanent lodging in our hearts.
Giving NPCs some Rooting Interest becomes a valuable tool in creating emotional immersion.