I believe it was originally intended so you could customize what is displayed inside the button.
But you can leverage it to execute actions inside the buttons as well.
in the tabs macro add the parameter for the buttonTemplate and point it towards a tiddler that you create to act as the template for the buttons. buttonTemplate:my-button-template
In the template tiddler place the following:
<!--- replace this comment with your actions -->
<$transclude tiddler=<<currentTab>> field="caption">
<$macrocall $name="currentTab" $type="text/plain" $output="text/plain"/>
You can wrap the actions in a list widget to make sure you execute the correct actions for the correct button.