I think it's great that CH has a fairly liberal and forgiving edit function. I often go back and read my posts to find that I've omitted a word, misspelled another, screwed up my syntax, what have you...
So I love that I can go back 45 minutes later and make changes of that nature, or, if someone asked for information on cooking or restaurants, come back later with more complete information and add that as well.
But I don't think it's cool when people go back and make material changes to their original comments that might have elicited controversial or unflattering responses. You can always add comments to clarify your position, or even admit that you might not have expressed your ideas as well as you would have liked in the first place, but to go back and make clearly material changes to your own controversial statements, and leave the resultant responses appear somewhat or totally nonsensical in order to save face is bad form.
What do you think the edit function should and shouldn't be used for?