I agree that a message needs to be communicated clearly and that whatever aids in the message's clarity should be used (or left out).

The example from your literary agent makes sense only in the context of scheduling a meeting--the day, time, and place (or medium) you have suggested. This goes, it seems to me, to a message's completeness. Sure, your agent is efficient as long as the agent's confirmation is held in the context of your request. But on its own, the agent's message falls short.

Grammar and punctuation should aid in concise and complete communication. I love the way many authors can skirt good grammar while achieving better communication. So I agree with your conclusion. Tim