I've never seen or read Game of Thrones but I hear that the author is in the habit of killing characters off quite frequently. I have no idea what these particular characters in the series are like (compared to the rest) and so it got me thinking about the differences between characters that a writer would want to keep in a novel and those that are disposable.
Before this point my thinking has been that it is only immoral (they got it coming to them) or uninspiring (they are no loss to anyone) characters in fiction that could be disposed of, but perhaps this is not so. I was also thinking that perhaps a character should only be killed off if it moves the story forward (they are a murder victim in a detective story) but maybe not.
So here's my question: what makes a fictional character in a made-up story disposable (i.e. what are his/her attributes) in a way that is satisfying to readers?
Research: I had a look at Is killing a character to further the plot necessarily a bad thing? but it doesn't really focus on what I need. Similarly, Killing off a character: deciding if, when and how looked promising, but the answers focused on the effect on the story of offing characters rather than what makes a character inherently disposable.