Why Use InfoPath Forms in Workflows?

Because each form submitted may contain different selections or entered fields, a workflow can look at the InfoPath form entries and perform actions based on those entries.

It is easier to have a submitted form living in a form library and having a workflow process around that form than to submit emails with attachments and updates and-files get lost and nobody really knows where the latest version is located. InfoPath forms provide a centralized location for the information being acted upon.