I sometimes see the wires of winding are twisted outside of the transformer (or inductor), as seen in the images below. What is the purpose of this? When should I twist winding wires and when shouldn't I?

![enter image description here][1]

![enter image description here][2]

(Note: This is not about using multiple twisted wires as a single wire inside a winding (i.e.; Litz Wire).)

  [1]: https://i.sstatic.net/jS5TP.jpg
  [2]: https://i.sstatic.net/E90vS.jpg