You shouldn't need a gust lock if the aircraft has irreversible hydraulic controls as the PFCUs will hold the control surface in position. With manual controls a gust lock will be needed to stop the surfaces slamming about in a strong wind and getting damaged. I don't know the ATR but the "gust lock on the throttle" sounds like the system on the BAe748. This has a gust lock lever in the cockpit which locks the controls. With the gust lock engaged you can't move one (or it might be both) throttle levers forward of the half way mark. This is to stop you inadvertently getting airborne with the gust lock engaged.