Structure widget is a real-time collaboration tool.
The issue hierarchy displayed in the widget is kept up-to-date with the JIRA server, so if someone else changes the structure on the server, you will see the web page update within several seconds.
In the same fashion, the values of the issue are maintained up-to-date: if someone edits an issue or otherwise changes it, the structure widget will update the displayed values within a few seconds.
This feature lets you collaborate with other people who may work with the same structure on different computers.
Structure keeps data up-to-date by polling the server with short requests every few seconds when the application is ready. If structure widget detects that the browser is inactive it will reduce polling frequency to conserve network traffic.