Exercise researchers say there is only one agreed-on fact about the possible risk of suddenly stopping intense exercise. When you exercise hard, the blood vessels in your legs are expanded to send more blood to your legs and feet. And your heart is pumping fast. If you suddenly stop, your heart slows down, your blood is pooled in your legs and feet, and you can feel dizzy, even pass out.
The cool-down is especially important for elite athletes since they have slower heart rates than the average joe and due to their high fitness level their heart rates return to normal quickly as well, making the pooling of blood even more intense.
I personally enjoy a cool-down period. It punctuates a hard workout and gives me time to transition into my next feat — be it navigating the kids' car pool or making dinner. What about you?