Auto Brightness actually waste more battery because the phone is constantly trying to adjust to the light... I'd leave it off, but have a toggle widget that can change ur brightness to a specified level with one click... It's easier and saves battery... There are plenty in the Play Store
Sent from my Galaxy S4 Exynos via Tapatalk 4... I LOVE THIS PHONE
I agree with smooth. Set the brightness as low as possible while maintaining a reasonable visibility. You'll keep the screen from constantly switching to the brightest setting, which isn't necessarily needed in all situations.