Consider the following Scenario:
A custom training session entity and enrollments entity has been created that link enrollees (contacts) to a training session which is being provided by a trainer (CRM user). If you want to send an e-mail that includes information about the training session, the product that it represents, the contacts who are enrolled, and include contact information about the person who set up the enrollment (owner) you will need to do this by generating a custom workflow e-mail rather than using a CRM e-mail template.
This example shows a simple workflow which checks to see if the training session e-mail actually needs to be sent, then builds a workflow-based e-mail with all of the details.
This email includes data pulled from four separate entities. By the way, the other cool thing you can do is to attach a document to the e-mail. You definitely can’t do that in the CRM e-mail template!