The Show Gists checkbox is on when checked, and off when unchecked.  It controls whether the story point item's name is shown, or the gist associated with that item, if any.  If the item does not have a gist, only the item's name is shown.

 

EXAMPLE:  Show Gists checkbox CHECKED (On)

 

 

EXAMPLE:  Show Gists checkbox UN-checked (Off)