I use the lowest at night and in class so i wont hurt my eyes or get caught, and 2 at other times how bout you guys?
I always use it at the highest settings since i NEVER take my DS out. I can never expose my treasure to dust and dirt.
Actually, 2nd is already bright enough for almost every indoor area. Highest is just for those who want to see crazy bright colours.
On the XL I use the lowest when I'm going to sleep without the lights on, but 3rd when lights are on and for anything else. Saves a lot of battery.