Hello Naufal,
This is a great question and the business model was recently updated with the ArcGIS Enterprise 11.2 and ArcGIS Online October releases. The service-based Workflow Manager has moved from a named user license model to an organizational capability license model so starting at 11.2 there is no longer a requirement for the Workflow Manager User type extension to be assigned to each user who will access Workflow Manager. You will still need to assign the Workflow Manager User type extension to each user in 11.1 and earlier.
Workflow Manager is a capability server in ArcGIS Enterprise and there are two levels: Standard and Advanced. There is a functionality matrix that lists out the differences in between the two, but essentially, if you want to utilize webhooks, job and step scheduling, and other advanced automated capabilities you will need the Workflow Manager Server Advanced. Once the capability server is in place, you can access the Workflow Manager web application from the Portal application tray (installed with Portal).
There is a Workflow Manager Pro extension available but it is completely optional. This is only needed for those users who need to access and work through jobs in Pro.
Workflow Manager Components and Licensing
Thank you,
Tiffany