The script will process the message body of the (selected) template message and replace certain tags by their corresponding value from the Address Book for each recipient. You may use custom data by specifing your own labels in the "related names" section of the persons Address Book entry (e.g. "Assistant", "Customer number", etc.) and the script will replace the corresponding tags by the corresponding Address Book values (Example: I use the script to inform students of their score (and other stuff), which is stored in AddressBook).
It is possible to attach personalized attachments to the generated emails: The path name provided to the tag "finder:file" can be parametrized with the recipient name. This allows to add an individual attachment specific to the recipient of the generated email. The path name may contain one or two placeholders defined by the two characters %@. The first occurrence of %@ is replaced with the first name of the recipient. The second occurrence is replaced with the last name of the recipient.