Each button references a template file that handles arranging functionality or might change the layout. With just one click you can trigger a template than can execute a sequence of commands that would otherwise require a bunch of of keys and/or mouse clicks.
Right-click on the toolbox to get its context-menu for modifying the toolbox contents (add/remove/change buttons etc).
Right-click on the toolbox-button itself
enables you to to select a specific toolbox.