You definitely do not "NEED" a chain guard. The benefits to having one is that if you over-lube the chain or use a thick lube, it will not fling all over your nice clean bike. The chain guard will also keep goof-balls from sticking their foot in the chain, but what are these people riding bikes for in the first place? Look at show bikes and race bikes....No guard. As for my bike, that chain is naked!
Lube your chain after washing, riding in rain, or every 600mi....
hope this helps.:thumbup