Multi/direct-post option have no effect

Hi,
I'm integrating commons-7.x-3.17 with external modules to build a site.
While configuring the sharethis module that comes with Commons, I wanted to select the "Multi-post" option that appears in
http:///?q=admin/config/services/sharethis# "Advanced" tab
Unfortunately, chosing one option or the other makes no difference on the visible result on screen.
Maybe I did not understand well how it should work. Anyway, I stay available for testing and investigating.
cu