It adds a literal **** tonn of mass to the train, without it there isn't enough inertia to get round the course.
That and it also moves the centre of mass towards the front which helps pull it through those rediculously huge inversions.
Strictly speaking, every coaster that has articulated trains instead of draw bars has a zero "car".
Each manufacturer refers to it in their own way but they all do essentially the same job and that is to provide a rigid support for the trains floppy end.
B&M got creative with their inverted, floorless and dive coaster trains by giving the job of the zero car to the actual first car, this is why the first 2 rows only ever move in the roll axis relative to each other.
I'm also curious as to what the second coaster is that they are referring to because as far as I am aware, Alpengeist is the only coaster full stop with a deliberately weighted support axle?