I rode flats for mtb until last summer when I dragged out the old hardtail and started ragging it. After 2 years of full suss, my feet just wouldnt stay on the pedals without them. Dont think I would ever ride HT flats again. I even raced the Ft Bill enduro HT clipped in. This is obviously a whole world away from super slack, long DH bikes. On my DH bike which is now slightly dated, I wouldn’t dream of riding clipped in, not because of the increased crash risk, but because of the body position it puts you in, and the fact bikes of that era are not designed for that style of riding. If I ever get a new DH rig, with new geo, I would stick clips on from the first ride.