I'm using the Photography workspace preset, but with the Layers sidebar and Tool Options pane switched so that tool options are on the LHS of the workspace, layers on the RHS.
In this configuration, the 'Hide the Tools sidebar' button on the toolbar actually hides the Layers sidebar (which is positioned underneath it), despite it being called 'Hide the Tools sidebar' when the mouse pointer is hovered over it.
It would make more sense if the name of the button were changed to reflect that it's now hiding the Layers sidebar, when the workspace layout is customised in this way.