This is to ramp the temperature up to 75°C (167°F). This denatures the enzymes and prepares the grain for sparging. the wort is typically recirculated at this temperature for 10 minutes.
The mash out step stops all of the enzymatic action (preserving your fermentation sugar profile). But as the Grainfather brewing units ramp up to near boil as soon as the sparge has started and you sparge with 75°C (167°F) water, the enzymes will be denatured. So it is good to ramp up to this temp before starting the sparge but this step can be shortened. This is typically done on all types of brewing systems.