There are no implications here, it's stated pretty explicitly: "Reference counts MAY be best done by putting a mutex around an integer variable, for instance.

There are no implications here, it's stated pretty explicitly: "Reference counts MAY be best done by putting a mutex around an integer variable, for instance. BUT as a high-level approach, using channels to control access makes it easier to write clear, correct programs." There is a difference between what someone with a background from other mainstream programming languages might think would be the best approach to locking (mutexes) and the idiomatic Go approach (unbuffered channels).