Video: Sometimes slow motion is used to enhance action scenes. Other times it's done to convey love between two characters. There are even times when it's used to replicate using drugs. Or show off a superpower. Or show dread. Or capture someone's last moment. The point is, slow motion is used a lot in films, for many different reasons. Here's a breakdown showing how certain directors use slow motion in their movies. Martin Scorsese likes to use it to put the audience in the head of his characters; we're able to see what a particular character sees because it's focused in slow motion. Wong Kar-wai uses slow motion in synergy with music, and also uses it to heighten emotion like the longing for love. Quentin Tarantino uses slow motion to make his characters seem cooler — but also to make you wonder which characters are going to survive the mess that is sure to come.
There are many more interesting looks at the art of slow motion in movies in the video essay by Julian Palmer, below.