it's safer. but not necessary. i built mine without one, in a carpeted room. i don't recommend that though. if you don't want to go through the hassel of buying a anti static wrist, just do it on a wooden floor or ceramic/linoleum floor, take off your socks and tap the power supply once in a while to make sure you're grounded. so basically, keeping one hand on the metal part of the case or power supply could be an anti static wrist. well, more like an anti static hand.