Some convenienece of exploring task list could be reached adding anchors to the rolled up folders (hiden tasks case). If you try roll it down to show all containig tasks, browser should scroll page (after reloading) directly to the rolled down folder. This could be very convenient especially in case where folder is at the bottom of long task list - no need to scroll all the page and searching rolled down folder.
PS.
We could imagine quite different mechanizm rolling down folders without refreshing all the page but it seems to be far complex than adding anchors.