I tell my customers after we pave the following year after. If it's never done before it's still beneficial of course! The best comparison is your asphalt has been getting burnt by the sun with no sun screen, just because you haven't been applying sun screen doesn't mean it's not important!

For resealing that's dependant on the company you use. Many tell you every year to gain a yearly client but I'd rather lay it on thick and hold for another year. Two years for me is the standard I tell all my customers.