Go at Google: Language Design in the Service of Software Engineering

The first step to making Go scale, dependency-wise, is that the language defines that unused dependencies are a compile-time error (not a warning, an error). If the source file imports a package it does not use, the program will not compile. This guarantees by construction that the dependency tree for any Go program is precise, that it has no extraneous edges. That, in turn, guarantees that no extra code will be compiled when building the program, which minimizes compilation time.