FIXED guns, There is no way to aim. If you slow down you hit the ground in your front, if you speed up you shoot in the sky. And to hit something you need to move perfect straight.
In real only planes and helicopter have fixed Weapons, and there it make sense.
You're right in that a fixed mount bullet-hose strapped to the front of a land vehicle would be pretty useless. You're also right about the mini-gun gor'ram jeep from "The 100" being pointless in a real-life combat scenario.
Here's my logic for adding frikkin' mini-guns to cars in the zombie apocalypse.
1) Z's don't tend to dive for cover, making them essentially stationary targets which are far easier to hit than something with a working pre-frontal cortex.
2) It wouldn't be too much of an engineering challenge to add a small lever for the driver to fine-tune the aiming of the gun once it's pointed in roughly the right direction. It would no longer be a truly fixed-mount at this point and would probably feel like the crazy aiming system of "Time-splitters 2" (damn I loved that game).
3) I want one
Definition of gubbins
1 dialectal, British : fish parings or refuse; broadly : any bits and pieces : scraps
2 British : gadgets, gadgetry
the gubbins for changing a tire
all the navigational gubbins —J. L. Rhys
3 British : a foolish or futile person : simpleton
you silly gubbins
I was going for definition 2. I've lived on this damn island for decades now and I've never even heard of definitions 1 or 3.