The official wear limit per Harley is 0.04" of friction material (not including the metal backing plate). IMHO that is cutting it a bit close unless you are in the habit of checking your brake pads on a weekly basis. I prefer an absolute minimum of 0.0625" (1/16"), and usually change pads at 1/8". It's not worth the tiny amount of money anyone would save by going to the absolute minimum, considering how much damage could be done if you wait just a bit too long and damage the rotors. Not to mention the lack of stopping power of course.
Btw, always check both pads on each caliper, inner and outer, and go by the thinnest pad. It's not unusual for one side to wear more than the other.
Jerry