Aerie Sage's main job is to support Aerie Stewards. This unit is incredibly good just in general though as it has decent stats but with an extremely good ability. The ability to give extra power to another unit without exposing itself is deceptively strong.
The main cost is that it requires movement to reposition which can be quite problematic.
Aerie Sages shine when they buff Aerie Stewards, but don’t be afraid to use them to buff Aerie Divers or Sentinels too.
Aerie Sage along with Aerie Steward are the core fighting power of Skyspear Avians and a cluster of them can fight toe to toe favorably with any army.