i think it's part of a chef's traditional working attire (hat, apron, jacket, etc) which included a necktie. I think it's just for looks, but not 100% sure
I don't think I have ever seen a chef wearing a tie. That would actually be dangerous in a kitchen as it could dangle over a flame or dip into someones food.
The proper way to wear these is to tie then in a traditional necktie knot then take the ends and fold them under the knot to the back and tuck them into the top of the knot so you have no loose ends. Very snappy.