how SKSpriteNode's node size affect performance?

when xcode generate texture atlas, it's load that texture atlas once.

my question is when texture atlas generating by xcode is he also draw it into memory and that's cause fast batch processing takes place when i assign that textureImage to skspriteNode object....???

when skspriteNode object created what happen when we addchild to sceneNode??? is spriteNode object node size matter and why should we place small size texture ???????

more in short what addchild do under the hood in scene,is he draw the texture ,what???