The idea isn't to 'find it'. The idea is to heat the area surrounding it. As Gary_R pointed out, it is more central to our core. The blood pulsing through your carotid is on its way to the brain, while the femoral is pushing out to a more wide area...= greater benefit.
http://ts3.mm.bing.net/th?id=H.47006...h=172&c=7&rs=1