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).
E.g. An bank account is shared state (similar to a reference count) and the best approach is to put a mutex around it instead of fighting with channel synchronization.