Workspaces allow you to save a configuration of your Obsidian panels and files. This is useful for when you have a configuration that you use regularly. I regularly need to open up my writing workspace which has a Kanban board and hides all the sidebars.
One of the other default workspaces I have is for my Daily Notes. Unfortunately you can't open up today's daily note with a workspace at this time so I have no note open and I reveal my right hand sidebar.