1) reduces errors and user frustration,
2) substantiates the thought in the user's mind that "the software will do what I want", and
3) teaches users that the software will accomodate them, instead of requiring the user to accomodate the software.
It would have been better, actually, if the dates also mentioned the day of week, like "Thursday, October 21 / Friday, October 22". I'm more familiar with what the day of week it is, but not necessarily what the date is.
If it mentioned the weekday, I would be able to answer "Thursday" immediately, since I know that I intended it for Thursday, but I wouldn't necessarily know that it was the 21st without looking at my watch.
If I'm talking to robots after midnight, I don't know the date. This has been proven by scientists.
> without looking at my watch