You'll notice plenty of comments here from people who claim to be principal engineers - stating that they "kinda follow it all". I wish we could talk to their colleagues though (the juniors, seniors, PMs, tech-leads, support/escalation engineers, as-well as other principals).
The company I'm at has a single principal engineer. He was hired externally. Within a year of starting, he'd had a bigger impact across teams than the CTO in the same time period. He doesn't necessarily write tons of code, but he's also not sitting in an ivory tower telling other developers what to do. Rather, he very quickly got in tune with the sorts of technical problems being faced by basically every team and developer at the company and started introducing various techniques and technologies to resolve pain points around the organization. Before long, we were doing things that wouldn't have even been possible before.
Documentation is such a mess because of that and the onboarding process specifically says there are a lot of "oral history" newcomers have to learn before doing anything meaningful.
Anecdotally, one of the distinguished engineers at my current place came from a similar role in Google. They left Google because they kept putting them and a number of other distinguished engineers on products and projects that would never see the light of day, or be turned in to an actual project.