It seems deliberately confusing to me since there is no fundamental difference between voting now and voting on the day of the deadline, but the way it’s discussed and referred to seems to imply that the correct day to vote would be waiting until the last minute instead of voting just getting it out of the way weeks ahead of time.
Not every state allows it and if they do it has to be a special reason in most states. So you must live in a lucky state or had an excuse every year