In Canada at least, it's as somebody mentioned: if you are required to have a radio, you are required to monitor 16. However even that is changing or has changed with DSC.
We monitor 16 unless we are in a tight traffic situation or planning on transiting a bridge or something, in which case we monitor 12, which is the port authority.
s/v Laelia - 1978 Pearson 365 ketch
s/v Essorant - 1972 Catalina 27