Bin Layouts made their debut in Media Composer version 6. Like Workspaces, they are a task-focused feature that, with just a visit to a menu or a push of a button, allow you to instantly reveal the bins you want and to have them arranged just as you've saved them, including in tabbed sets.
Bin Layouts can be activated independently of Workspaces, or they can be activated automatically at the same time you activate a Workspace. Avid refers to this as linking. That feature is covered in the Linking Bin Layouts with Workspaces and Mapping Workspaces and Bin Layouts recipes.
An important note is that Bin Layouts are not saved as part of your User Settings. They are actually specific to a particular Project. See the There's more… section in this recipe for additional information on this.