Disadvantages -> Timezones
Timezones make scheduling team meetings hard, and if your organization ever becomes big enough to warrant a physical office people far away will start working late hours to keep up with the main office.
YMMV, but it's 3 AM here in Berlin and until 10 minutes ago I was still actively working.
You need the synchronous communication to have non-work conversations, and you need those non-work conversations to develop and maintain the relationships required (trust, rapport, etc.) for remote work.
> if your organization ever becomes big enough to warrant a physical office
...then you probably don't have enough buy-in to be a fully remote company and that is far harder to work around than timezones.
Sounds like an unhealthy implementation. I've worked 12 hours apart from a main office for 3 years and never worked past my local business hours.
See written & async first communication. Mailing lists work for things like linux kernel development.