The value of the Makefile is for automating repetitive dev tasks. Consumers of a golang CLI should use `go get` but this makes it easier for contributors who run tests, cut releases, ..

The authors example is clean/simple. Here's an example not so clean/simple example where we needed to do more complex stuff like build for all target platforms[1].

[1] https://github.com/cloudfoundry-community/stackdriver-tools/...