I see adding "EDIT" as a nice way to show what was changed, even if it was just a typo (though if I'm fast enough at catching a typo I won't always add "EDIT"). It helps people that already read your comment so they can see what changed and prevents confusion. For example if someone edits in a link to what they were talking about or adds context I really appreciate the "EDIT" because without it I might skim over their comment without noticing the change if I've already read it pre-edit. People who make big changes to their comments without mentioning what was changed are being somewhat disingenuous in my opinion. Especially if they change their viewpoint significantly without calling it out. It's a bit of an asshole-move especially if people have already replied to your original comment.
> My impression is sometimes we could just edit typos and small stuff, without the need to make a disclosure at the bottom.
Yes, I would generally agree with this.
> Some would even keep the original text intact and state corrections at the bottom, which renders a worse reading experience, in my opinion.
This is a grey area for me. It's somewhat hard with HN's formatting to transparently and clearly fix the original text sometimes. Example: "I do agree" -> "I do not agree", do you put "I do (EDIT: not) agree", "I do not agree (EDIT: previously typo'd that I do agree)", "I do agree \n\n EDIT: I actually do /not/ agree, that was a typo", etc. I think people that leave the original text and then add a disclaimer/correction at the bottom are attempting to be open and transparent and I respect that. There used to be an HN plugin years ago that did edit diffs on comments (displayed them kind of like git diffs) and I do kind of wish HN would show edit history. I've been burned by replying to a comment that gets edited out from under me such that by the time I comment they are no longer making the point I'm rebutting or they've softened/changed their argument. Because of this I often will quote what I'm replying to in these cases to protect against the author changing their comment and making mine look odd/out-of-place.
> Sometimes I edit so fast after I published that I doubt anyone has read it before I edit.
I think this is fine, as long as you aren't changing the spirt of the comment. Typos, link adding (if fast enough), and similar are fine to do without calling out the edit.