Business notes support you politically and help you get your work done. I do not completely agree with Isaacs about e-mail being so impersonal and losing the warmth of human contact. An e-mail can be worded effectively to establish and keep contact. E-mail should be valued for its power of persuasion. My wife is particularly skillful at saying just the right line when she has to write a business note.
People remember well-written business notes, regardless of their form.
To me business notes require your picturing how the other person would react to your words. Florence Isaacs classifies follow-up notes as part of business notes. Suppose you are the person in charge of obtaining a speaker. People like to be acknowledged for their efforts. So few people thank that, usually, the individual is touched to receive a personal acknowledgment.