How often they sharpen depends a lot on the type of work. Generally during that first six weeks they're touching up chains once a day or once every other day. We have a test log they'll make cuts in to evaluate their sharpening. We're looking for nice big shavings of wood instead of powder/dust.
The main bad habit that comes from working with a dull saw is putting way too much pressure on the saw to push it through wood. People will get used to forcing a saw through limbs for instance, then when they get handed a sharp saw the bar is zipping though the limb and ending up a foot or so beyond it. If they're in a good position where their legs aren't in the bar path, it's no big deal.
It's also a big concern with falling. People who are used to putting in back cuts with a dull saw can easily zip right through their hinge wood if you hand them a sharp saw. A slow back-cut on a tree with heavy head lean is also a recipe for a barber chair, where the trunk splits vertically.
