Let’s say a grape variety normally takes 120 days to ripen. In an especially hot year, it may ripen after only 100 days; in a cooler year, after 130 days. Which situation would a viticulturist prefer? All other things being equal, viticulturists want a long growing season. Long ripening (a long hang time) allows components in the grape other than sugar—tannin, for example—to reach greater physiological maturity. Fully developed grapes, of course, hold more promise for a wine with fully developed flavors. Historically, perfectly ripe grapes that took a long time getting ripe often produced superior wines with more complex aromas and flavors.
(For complexity, I always imagine the deep flavor of freshly squeezed orange juice from ripe oranges versus the shallow flavor of powdered mixes.) There’s one important distinction here. Long hang time in the pursuit of ripeness (a good thing) is not the same as overripeness (a bad thing). When a wine has all the charm of prune juice crossed with flat cola, it isn’t pretty.