It doesn’t matter if it is business or personal. Accidentally sending an email that you have not finished writing is embarrassing and potentially damaging to your personal life and/or career.
I just made this mistake three minutes ago, possibly for the first time ever. I was belaboring the process because someone was having hurt feelings and I am always uncomfortable about that kind of thing. Belaboring for me involves saving drafts and surfing the net while I procrastinate. The last words that I typed were ‘Please don’t’ , it doesn’t get much more awkward than that. I pressed send instead of save. Save is the word I would use to describe the very quickly written follow up email.
Catherine told me after the fact that she often leaves the ‘To’ field blank in order to avoid this kind of accident. That’s very good advice.