save one's breath
Refrain from arguing about a lost cause, as in You can save your breath; I'm not going to change my mind. This term was also put as save your breath to cool your porridge (or broth), that is, by not blowing on the too hot liquid. The idea of not expending one's breath to say something another person doesn't want to hear dates from the early 1700s.
too many cooks spoil the broth
Too many persons involved in managing an activity can ruin it, as in Without a conductor, every player had an idea for how the music should go-too many cooks spoil the broth . This expression alludes to each of many cooks adding something to a soup, which finally tastes awful. It was already considered a proverb in 1575 (by George Gascoigne in The Life of P. Care).