Here it is written that you need to use a lock for some actions
http://www.whitehatbox.com/bbs/bbspost?postid=4944#.WWPYaBXyjMw
These actions are listed:
Upload File, Mouse Emulation(web), KeyStrokes Emulation, Flash Action, New Captcha
Is this all the action for which you need a lock or lock is needed for something else?