Presentation actions are only rarely needed. Often a presentation-to-command translator is more appropriate. One example where actions are appropriate is when you wish to pop up a menu during command input. Here is how CLIM's general menu action could be implemented:
(clim:define-presentation-action
presentation-menu
(t nil clim:global-command-table
:tester-definitive t :documentation "Menu"
:menu nil :gesture :menu)
(presentation frame window x y)
(clim:call-presentation-menu presentation clim:*input-context*
frame window x y :for-menu t))
Common Lisp Interface Manager 2.0 User's Guide - 20 Sep 2011