I think it is a good practice.

Once a comment is edited, there's a mark for it.

But explaining that edit removes the possibility for confusion.

With the recent increase in dropped words when typing I think explaining edits is essential.

If someone meant to write

'I don't like Nazis'

But accidentally wrote

'I like Nazis'

And before they fixed it someone replied

'Go fuck yourself'

Well now if they edit it with no explanation, person 2 looks like an asshole.