Question

Much of our language use serves non-informational purposes, such as

Answer 1

The answer to this question is Establish and maintaining social relationships.
We are more likely to be liked or accepted by other people if they could understand our intention. And they will tend to understand more if we and those people speak the same language.
Maintaining social relations could simply be done by simple greeting and smiles every day, so it does not need to be informational.