Gunnery training! This is probably the most time you’ll spend in a turret throughout the game. The sad truth is that while manning a gun turret is kind of cool, it’s far more effective to just set the turrets in defensive mode or to attack a specific target, than it is to turn piloting over to the droid and jump in a turret.
But it sure is fun to feel like Luke Skywalker or Finn and blast TIE Fighters from a quad laser battery!