You do get a last chance in preview. It’s easy to get overconfident and check the box. If I were king, I would force anything having HTML in it to go through preview.
I always post with HTML and always read the preview. Sometimes that isn't enough. When you write something, it's possible to have your mind "fill in" the missing parts when "proofreading". You see what you want to see, not what is actually present. The final post appears a bit different from the preview. Sometimes you spot the goof at that time. It's too late.