In the office, instability is generally considered a handicap. In the gym, according to this piece in the Washington Post, it’s a way to jack up the benefits of a resistance workout. Howard Schneider reports on the several advantages of adding "complexity" to a workout. "Complexity," writes Scheider, "whether in the form of unstable surfaces that challenge
balance during exercise, or dynamic movements that involve more of the
body — can produce a variety of benefits. It strengthens the core
muscles of the abdomen and back, helping lessen the need for a separate
abdominal routine, and burns more calories than conventional
weightlifting."
Read more about the benefits of instability in the Washington Post.