The notes field in OmniFocus is got for more than just text. My daily routine article had some suggestions about how to link in applications, folders or documents to OmniFocus tasks or projects.
Christopher Mackay’s post covers a very specific use of the note field. With some Finder magic, as explained by Christopher, you can access individual mailboxes of Mail.app and link to them direct in OmniFocus. Checking you spam inbox once a day as illustrated in the post is only one possibility.