Electric hook-up cable

Have been reading the technical question and answer page in this months` club magazine regarding whether to coil the mains hook-up cable while in use on the site.  It does state how dangerous it is to leave the cable still coiled on the reel as there is a serious risk of its insulation melting (with consequent risk of electric shock) or even catching fire.  It made me think as I see cables still coiled on their reels so often on sites.  I always lay the cable out along the ground.