After installation, Jira Administrator can decide if the graph should be visible or hidden by default (3). It could be done within Add-ons section on Settings page (under Issue Links Viewer tab):"Apps" (1), after accessing "Settings" (2) (located under the "Issue Links Viewer" section):
This setting can be overwritten by user preferences - even if the graph is hidden by default, it can be displayed after pressing "Show links graph" button (1):
Expanded graph can be hidden again via "Hide" option in the top right corner (1):
