Workflows can have two different states - Live and Draft. The Live version of a workflow is what will be ran if you are using the Runs Table, API, or Magic Form.
If you make an edit to a Workflow, this creates a new version of the workflow called a Draft. You can make edits and Test from the Build screen. Any Test you run will return the results of the Draft version of the workflow, but anybody actively using the workflow through the Runs Table, API, or Magic Form will continue to get results from the last published version of the Workflow - the Live version.
If you see the purple Publish button present on the build screen, that means that your workflow currently has a Draft version and the results from the Test output may vary from the Table, API, or Form output.
This allows you to update and test a workflow without making potentially breaking changes for everyone else, only publishing when you’re ready to make the Draft version the Live version. After you click Publish, everyone using the Workflow through any means will be getting results from the latest version.