This has been on my plate for a while and to be honest I’m not sure what took me so long as it literally took around 4 hours from start to completion which I consider a testament to how easy it is to create additional integrations with PowerShell akin to the Gutter integration or the login/logout integration Michael West has recently introduced in the platform.
What this integration allows you to do is to eliminate the need for code deployment when you’re in need for a quick action here and there for when a user executes a workflow command.
You might find this article helpful by a Cognifide colleague of mine. I especially like this image which illustrates nicely where actions fit in a Sitecore workflow.
They are effectively little bits of code that get executed automatically when a user triggers a command.