house,
Primarily, fluting gives the barrel more surface area for cooling. It looks cool is a cheap second reason. It's really more for "eye-candy" than for anything else. Once one manufacturer comes out with it, they all have to. Understand that perhaps a varmint shooter who caps dozens of dogs or coyotes on a single outing may find that the heavier, fluted barrel may offer him some additional cooling, but not enough to warrant spending the extra money to look cool. For common fodder like deer, moose, bear and such, a standard tapered barrel does just fine and is just as accurate in the right hands. Accuracy is a combination of shooter technique, experience, wind conditions, heat/cold, and the weapon being in prime condition. I know an old guy at the range that I frequent with an old H&R single-shot that outshoots most anybody I know with those fancy custom rifles. It's all about practice, practice, practice.