Difference between adding sprite to the game and scene or state

Phaser 2 / CE
1 
code is written in a state class

which of the following is the best pattern to move on.?

let image = this.add.image(x, y, key);
                 or
let image = this.game.add.image(x, y, key);
2

They’re identical, both add the new sprite to game.world.

3

but why like that there should be some differentiation know ? any how thank you dude for your time.