The Professional edition is a great fit for any business user who needs to do automation, data extraction, or web testing but doesn't need to integrate with other applications. It allows you to do straightforward tasks like login to a website, navigate to a page, and e.g. delete forum postings (which includes several clicks like: "Are you sure?", "Return to forum", ...)
By comparison, the Enterprise edition includes the powerful iMacros API (scripting interface) and support for iMacros Players. It is designed to enable complex automation, extraction, and web testing workflows, as well as seamlessly integrate with other tools, testing suites, database systems, and other back-end processes, e.g. web servers.
The Enterprise edition includes five iMacros Players licenses, which you can use to run macros from different locations across a single organization. For example, let's say you write a macro to assist your order entry team. You can use the player to load and run the macro on every order entry workstation.