To give more control over how many days out people can book, be able to identify "days" as business days instead of calendar days.
Example: If I want to limit my calendar to only 2 days out (to optimize appointments and minimize no-shows), but my availability is Monday through Friday, people go to book on Friday won't see any days available beyond Friday (because the other 2 days are Saturday and Sunday - of which I'm not available). So, to get around this, we have to set the availability to 5 days. That means, if someone goes to book on Monday, they'll be able to book all the way until Friday - which is too far out and increases no-shows.