Its part of writing code that uses THREE.Vector3 and doesn't pass in every parameter separately. Which really reduces the redundancy when you need to have decently long variable names. Aliases are just confusing and unneeded, they could lead to unintended conflicts, and force you to have to read more code.

You can use aliases, but you are probably never going to convince me :D .

I am surprised Kevin you are against using functions to call functions with parameters Kevin, this is Javascript, you got to embrace the functors :P .