not sure what kinda of turret defense are you talking about but.
Hardpoint turrets have three firemodes,
Forward fire: Acts as fixed hardpoints pointing front
Target only: Self explanatory, will track your targeted enemy even if out of your pilot field of view. (there are some issues associated with this turret mode though)
Fire at will: self explanatory as well, will automatically fire on any enemies you are ENGAGED with. Which means you have to engage the enemy in either forward fire mode or with another weapon first.
Point defense turrets: Will automatically intercept missiles and hatch limpets.
Chaff launcher: you have to fire these manually, dont have to set a firegroup but you can. You can use the chaff shortcut in the key binding options. It functions like a SCB