It adds support for motion NBT to the world, which makes your mini-game maps easier to make.
Add tag to what entity that you want to move.
here are all the available tags:
-"mot" : Throws entities in the direction of your gaze
-"random_mot","random_mot_mid","random_mot_big" :Throws entities in the direction of your gaze, but adds randomness
-"one_random_mot" : Add randomly but it doesn't work when applied to multiple entities
-"random_exp" : throws entities to a random direction, if you do this to multiple entities at once, then it will look like an explosion!
-"trace": Throw entities to the nearest player
-"away": Throw entities away from the nearest player
Here's an example of throwing a snowball:
/summon snowball ~ ~ ~ {Tags:["random_mot"]}