Speaking is inefficient:
- I could mis-hear and copy it down wrong
- I have to spend time listening to you and writing it down somewhere
- If I'm not in front of a computer then it's written on a piece of paper, I have to store it somewhere for future reference, or spend more time typing it up
Email is efficient:
- You've got a record of the information for the rest of your life, with no further effort (you are using a web-based email system, right?)
- You can search for and find the information instantly
- You can forward it to someone else for their reference
- You can copy and paste with no chance of error
- Email is so fast that someone can email you while you're speaking on the phone, and you can receive it and verify that it's correct before they hang up