It's a event risk x measure of damages x wearing discomfort calculation. Everyone weights these factors differently.
It's long since I had the last fall, not doing crazy jumps n stuff, prefer to keep in contact with the ground, thus for me the event risk is low, but I ride pretty fast, thus the measure of damage IN CASE of a crash for the head/spine is high enough for me to compensate for the little discomfort -> no pads, but helmet and backprotector.
5"8 / 125lbs / +27/+9 / Jones Flagship 158 and Ride Farah 153 with Ride Fame
The average human has one breast and one testicle