(I believe all the suggested duplicates are to do with having a cancel button at all.)
I frequently post to Stack Overflow on a flaky mobile connection. It's far from unusual for me to think of an improvement to an answer while it's taking a long time to save an edit or the original post.
Unfortunately, if you click on the "cancel" link while the save is hanging, it doesn't cancel the save - it cancels the whole edit, losing whatever I've already done. This has bitten me a number of times.
I'm fine with "cancel" meaning "I don't want to make this edit" while I'm actually editing - but while the current logical action is "upload this edit to the server" I'd really like "cancel" to mean "abort the request and let me go back to editing."