The ability for us as developers who are not networking experts is very simple! You create an envoy file in YAML format which describes how connections should be routed through our system (think IP addresses).
This allows me at least some degree of confidence when deploying new code changes because we know exactly what will happen from one change point until another without having full visibility into all details regarding where packets actually go within my infrastructure stack - this was previously quite difficult since there were so many moving parts involved.