There's all this discourse about "you don't need to say thank you to AI" (Sam Altman said it costs a fortune). I agree with the economic perspective, but there's something deeper.
LLMs are trained to complete threads based on data collected from the internet. Conversations where people say "thank you," "not quite," "we're getting close but..." have different continuation patterns than ones where people are terse or dismissive. These gestures are in the training data, so they will influence how the model continues your thread.
In anything longer than a very short exchange, your tone and feedback signals genuinely help steer the agent in the right direction.