A Shake workspace is a hub where you and your team members work together on your apps. For example, if you decide to upgrade to a Premium plan, the "thing" that gets upgraded is the workspace, not your user account.
Create or join multiple workspaces
Since workspaces provide clear separation of data, creating a second or third user account will never be necessary.
So, if you work in multiple teams or want to keep apps separate for any reason, feel free to just create or join as many different workspaces as you'd like.