Does everybody use a -3dB pan depth?
Meant to respond to this sooner. -3dB is the default because of it's relation to power level and phantom imaging. If you want a full strength image centered between two sources, the crossing point of two "equal power" curves needs to be at -3dB. If it's lower, it will sound weaker as it moves through the center point of the image; higher, and it will sound stronger. -3dB just helps you maintain that even stereo field.
As such, I don't mess with it in my DAW's settings. ;)