Practicality of codebook in current-day secret communications
I believe the possible advantages of the principles behind a codebook are:


Can be memorized by humans.
Can be used in normal speech (e.g. over the phone/radio/in normal conversation) or in text (e.g. in a newspaper)
The data is compressed: it can replace longer phrases or concepts with shorter ones.
Plausible deniability: It's possible to deny any code exists at all.
As long as a specific code is only used once and the codebook is kept secret, it's perfectly secure.


So some uses would be for:


Military operations (e.g. "Execute Plan A" would be meaningless to enemies and also allows faster execution of the plan than having to detail it)
Communication to people with no high-tech equipment, e.g. resistance groups with only access to radios/tv.
Groups of people who want to stay anonymous referring to each other by a nickname.
Criminal organizations who do not want to be openly on record talking e.g. about drugs or plans.