The question really relate to stop-bars. The use of interim hold-shorts is for traffic management, sequencing, separation. As I understand it a determination was made by SACL, Airservices, Industry and CASA for the stop-bars to be active all the time. This is different to how stop-bars are operated at some locations (only used at night or during reduced visibility). Conditional (runway crossing) clearances were scrapped with the introduction of stop-bars so this has slowed things down. Some ATCs (minority) will issue multiple crossings at say TWY Charlie and then monitor the lights to drop for the second and subsequent aircraft, other ATCs (majority) will wait for the stop-bars to come up again prior to issuing a runway crossing clearance.