Board Thread:Episode Discussion/@comment-26299202-20180110014145/@comment-26397825-20180113130942

Aura protects you from injuries if you kow they're coming or have enough left. Sienna and Vernal both got blindsided and killed with no aura damage, despite the fact that it would be stupid for either of them not to have their aura unlocked.

They've already stated that aura helps with healing, as a cut that Jaune got when his aura was locked healed up no worries. It depends on the severity of the wound, as shown by both Weiss and Blake healing with scars. Just because your aura drops doesn't mean it won't affect cuts and wounds after it comes back.