Racking the Radiator was a mud riding thing, but it can be used at any time. While not that needed for a regular trail riding ATV, it most definitely helps with keeping engine and coolant temperatures down. If you ride in a really hot climate, or do a lot of slow speed towing, crawling or heavy working of the bike in warmer temperatures, a racked rad can sometimes make the difference between a overtemp situation or not.
Unless your having issues or going to ride lots of deep mud, I wouldn't bother racking a rad. Your bike was designed to operate without it in normal conditions, so it's not really required. You lose your front rack space, and it's just something else to break if you accidentally roll it.