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.