The workspace in Power BI are the containers where you house dashboards, reports, workbooks, and dataflows that are created using Powe BI.
There are 2 workspaces that exist, My Workspace and Workspace. My Workspace is just that, a personal workspace environment that you create and work with your own content that you have loaded. Good news, you are able to share dashboards and reports that you create in My Workspace. However, the content created in My Workspace is not interactive or have the ability to be collaborative. For collaboration and interaction, you will need to create a Workspace.
Workspace is where you can work and collaborate and share content with others. Just know, to collaborate, the person that you add to Workspace will need a Power BI license Pro or Premium license.
Workspaces also allows the user to create, publish and manage apps. The Workspace will make up the Power BI app. The Workspace feeds the app with a collection of dashboards and reports built for the key metrics that an organization presents. The apps are interactive, but those who have access to them are not able to edit them. Another unique feature is those who have access to the app do not necessarily need a Pro or a Premium user license.
So, as you create your dashboards, reports/visuals and workbooks determine which level of workspace is great for your organization to share and/or collaborate.