Affects how wide the end of the sleeve is on some garments. There is no effect for sleeves ending at the biceps or above. For longer sleeves, the wrist measurement and this wrist ease option have a progressively larger effect, reaching full effect for long sleeved garments (sleeve length of 100% or greater).
You should use negative ease if you are using a stretch material that you want to fit tightly. Unisuits and unitards typically have negative ease, while other garments typically have positive ease.