On certain cars (perhaps even most? all?), such as the old Toyota MR2 turbo, there are multiple ground points. Some of them are described with pictures here: http://www.mr2oc.com/59-general-mk2-faq-newbie-center/408099-engine-bay-ground-pics.html
I naively thought that these are for redundancy, but after failing to connect one of them after performing some work, I found that the car would not start.
Why are there multiple ground points, and what could cause the car to fail to start? In the case of the failure to start, the missing ground was for the ground on the intake manifold.
I've even heard in a video giving an overview of the E153 transmission that failure to connect the ground on the transmission (why does the transmission have its own ground? Is it not physically connected with conductive metal to the engine?) can cause a fire. Is there any merit to this claim?
This is the video: https://youtu.be/bbgY7hygM0c?t=31s