The biggest advantage of booking months in advance is that you get your dates and the boat you want. This is important for school holidays if you have children, or other restrictions. Then you can tract airline prices and lock in at a rate you are happy with. Wait too late and airlines fill up/ prices increase.
As an owner, I offer discounts months in advance. I also offer additional savings for "last minute" bookings. Generally 2 months in advance. For example, I have 2 weeks in June /July that would get a 35% discount.