Many resorts, to save money, will make comparatively deep, wet, heavy snow once or twice a season on any given trail, then call it quits for snowmaking. All further snow conditioning relies on Nature and grooming. But unless Mother Nature is in a bountiful mood, this type of snowmaking allows resorts to do little more than simply open the trail. While durable, heavy, dense base snow doesn't generally result in the lighter surfaces most skiers and snowboarders prefer. So after a given resort's ability to control the type of snow they make, the second most important factor is the frequency with which snow is made.
Fresh snow is simply more fun to ski.
There's a reason why our resorts make snow on a regular schedule. For one thing, snow wears out. Smaller crystals pack more tightly, which can lead to hard surfaces, and can't be aerated by grooming machines as effectively. Refreshing the snowpack on a regular basis, either with machinery or nature, is the best way to keep surfaces fresh. Ski areas typically claim to be able to cover a large percentage of their terrain with snowmaking.