In the majority of the races I run, blisters and chaffing are rarely a concern for me. Anything under a marathon in normal temps/climes I never have to worry about things rubbing and causing issues, think shirt on nipples, inner thighs rubbing, your feet, etc. However, each time I've taken a foray into the ultra running world or one of the smaller trail races with weather or water on course, I will usually end up with something chaffing or blisters on my feet. Let's face it, if you rub a prune against something long enough, it's skin will rip open.
So what's a guy (or gal for that matter) to do on race day when weather is imminent or you are going to sweet like a stuck pig and you know things are going to rub? You reach for some kind of lubricant, much like greasing up parts on your car because metal rubbing against metal for too long might cause some fire.