Teammates need to use the same language so that everyone is on the same page constantly.
This can be achieved through an official Handbook that encloses teams' guidelines and best practices.
That way, people can focus on the essential things without worrying or making constant decisions about all these little details here and there.
The absence of an official Handbook may lead to randomness and conflicts due to personal preferences and lack of guidance. Conflicts disappoint people and nobody actually wants this.
Last but not least, the official Handbook helps new-joiners to accelerate and grasp how the team works straight ahead 😉