What is saying חַס וְשָׁלוֹם (chas v'shalom) supposed to accomplish? Does it do so, or is it just a waste of breath?
Based on the answers given to my previous question about this phrase, it seems likely to me that it serves as a prayer that bad things not occur. But I'm here seeking any source that indicates as much or that indicates any other reason to say it or what it accomplishes.
Relatedly — and this may be wholly answered by the answers to the first part — what is חַס וְשָׁלוֹם to be said regarding? I've seen or heard it said about
- things that one hopes will not happen ("if his cancer is to come back, chas v'shalom"),
- things that would have been bad had they happened (but they didn't: "if I had been sleeping, I would never have smelled the gas, chas v'shalom"), and
- things that can't possibly happen ("if God didn't exist, chas v'shalom").