Large code bases can become increasingly complex to manage as you add more code while also refactoring what is there already. Even with diligent code reviews, it is easy to gloss over common programming mistakes. Sometimes code can be written in a simpler way. Or perhaps a recent refactor left a few functions in that are no longer used.
Luckily the go tool includes a sub-command that will examine Go source and report suspicious lines based on heuristics that the compiler will not catch.