There are 3 main benefits to having an up-to-date calendar: search ranking, guest experience and reliability.
Search Ranking - Updating your calendar regularly leads to more accepted bookings, which will have a positive effect on the position of your listing in search results.
Guest Experience - Keeping your calendar updated allows potential guests to see the correct information about your listing’s availability and pricing. If your calendar and pricing are not up to date, guests will have a negative experience and are less likely to book or recommend your listing.
Reliability - An up-to-date calendar reflects that you are a reliable and trustworthy host.