if you use player setVelocity [0,0,10] on a player, they will take damage and play an animation that appears to be associated with being hit by an explosion. If this command is used on an npc instead, the npc is launched at 10 m/s into the air. I'm not sure which of these behaviors is the desired one, but it would be nice for the command to be consistent. As a point of utility, it would be nice to be able to use setVelocity on the player in order to make them fly, or perform some other velocity type of action. Hang glider or segue or something, maybe?
Note that higher values, such as 25 for the y component will result in death of the player and them being launched a very short ways as if they had been standing on explosives when they detonated.