From Rise: The Vieneo Province

The first and foremost important purpose of a hanger is a safe location for ground crews to work on and upgrade vehicles.
Possibly including:

  1. Engine overhauls
  2. Replacing engines with custom ones example more power, using less fuel or lighter.
  3. Moving weapons from one ship to another.
  4. A hanger can be used to store aircraft and aerospace vehicles during inclement weather.