Having a sharp blade on a chainsaw not only saves effort and wear on your equipment but makes using it more safe. Besides, dull chains won't cut straight.
Manufacturers recommend checking and readjusting chains often, especially when first using a new chain (the break-in period). Wear gloves and safety glasses/goggles during the sharpening process. You are dealing with extremely sharp edges, and without gloves you could easily cut yourself. When filing by hand, there's no need for goggles. As you might expect, manufacturers do recommend using their own oil, chains and bars.