It's useless to be honest.
I've yet to send or receive any important message or conversation with the in-game CB. Unless you're using CB for convoy, nobody really uses CB for anything useful other than screaming, complaining or blasting music, at least on the default channel.
Not to mention not everybody speaks English. So even if you want to, you can't talk to many players roaming across the street.
Also, I've yet to hear any mod or admin ever use CB. Everyone just prefers text chat (even though it's difficult to text and drive).