More Info here. Github Link
Basically preloading of filament to save time 
They could, but they didn’t. Why? Because you don’t want the filament to stay at the tube without doing anything too long. For example if you have 200 layers before the second filament /nozzle get used, and you preload the filament, then it means that it has to be stretched, twisted, bent for 200 layers, easy to cause a break in tube accident.
And loading during the toolhead is running would cause unwanted and hard to compensate vibration, significantly reducing the printing quality. The filament breaking through PTFE conenctors and getting into the extruder/haul effect sensor can cause significant “knock” and you won’t want that knock to happen on your toolhead when you’re printing.
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