Enterprise Vault can be configured so that a mailbox or public folder item is archived only if the item has an attachment, assuming all other archiving criteria are met. This is not the same as archive attachments only.
The advantages of archiving only items with attachments are as follows:
A significant performance improvement, since many fewer items are being archived.
Fewer problems generally, because fewer items are being archived. For example, users open fewer archived items, there are fewer problems archiving items, and so on.
Normally, using the "leave cover note text" option means Exchange store growth for messages without attachments. However, if you set this and also configure Enterprise Vault to archive items only if they have attachments, then Enterprise Vault leaves cover note text only for items that do have attachments. This means that there is always a space gain.
The disadvantages of archiving only items with attachments are as follows:
You cannot use this method if you are archiving for legal reasons because you cannot be sure of what will be archived.
Users will not be sure of where to find older items. Should they search in the mailbox or in Enterprise Vault?
Such a policy may be harder for users to understand than a simple age-based one.