It seems this pref was added...temporarily? It has a large warning: (WARNING! This increases server load significantly; if performance is a concern, use the update_totalissues.pl cron job to update the total issues count). The bug report seems to indicate use of DOM of GRS1 should make this unnecessary. With plack as well I wonder if we need this warning which essentially ensures no one will enable this.
The warning is due to the fact that UpdateTotalIssues is called in C4/Circulation - this routine can take some time - so likely should be moved to a background job - that or bug 20418