It's a freeform text area where you can add your own notes about the clip you are making. The content will show up in the note separated from the clip. It's risk free to try it and see what you can use it for.
1) Joe can go to the business site and enter his work email to get auto invited to the business account.
2) When we confirms his email address and clicks the link to activate his account he will be asked to:
a) Sign in using his existing account (recommended)
Create a new account.
3) If he joins the business with his existing Evernote account he can
a) Add his work email address during the join flow
Add his work email on the settings page. (there is a field 'Business email' on the 'Personal settings' tab
Essentially this allows users to have 2 email addresses associated with their Evernote account. The business email address will be used for all interactions with business content. I.e if he emails a business note the sender address will be what he enters in the 'Business email' field.
If Joe is already Premium he will get a gift card covering his remaining balance sent to his personal email. Once fully joined the business account will be charged for his seat.