/diy/ - Do It Yourself

Hello /ohm/, /3dpg/ tourist here.
First, what's the point of these big fuses in pic related? As most boards seem to do well enough without burning down your house these days, are they even necessary?
Second, considering every driver breakout board comes with a potentiometer to adjust to your motors, how do these kinds of board without potentiometers work? Do they just kinda average the reference, or is in this example Prusa basically locking everyone into their specific LDO motors?
Last, but not least, given there's 1 driver for two (z) motors, doesn't that mean that particular driver is stressed far more than the others or is there some kind of duplicating magic going on here?
If haven't already, please do assume me a moron. I'm just trying to finally catch up on electronics and see if i can make some sense out of my prusa in comparison to other machines.