Many VR experiences use the "floating hands" technique, which is effective but not exactly natural-looking (or -feeling). Arm tracking allows developers to take advantage of common movements and accessories, such as blocking a punch or wearing a Pip-Boy -- or an Apple Watch, if you're into more realistic experiences. The Manus team is still experimenting with full-arm tracking on the Vive, but it will be featured in the gloves' SDK that's due to launch in June.