I use Auto run very often as I play with a PS3 controller (to prevent joysticks being worn out so fast) o:
Its also helpfull when on a mount! You can fly to a location and do something else meanwhile.

Auto run stops if you do an Atk-Skill (it also stops if you press again L1)

Im playing 2years now. Im pretty used to it with hold R1 to change skill bars o;