Fan Casting You Have Outlived Your Usefulness in Sort by Tropes

To show or remind the viewer how nasty the Big Bad or his Evil Minions are, a common trope is their habit of callously disposing of anyone who is no longer useful to their plans, whether it be an associate of an evil organization who has just concluded their useful function within that organization, or an outsider whom the villain has coerced or tricked into carrying out part of their plan who is killed once they have done what the villain has ordered. It is often punctuated with words to the effect of "Your services are no longer required", "you have served your purpose", or of course the title phrase before the murder.