Hill style form generally involves a slightly bent elbow. How much depends on the individual and the grip on the bow. Some folks can get away with no guard, others can't. Even those who can can get zapped if they're careless. Not to be a wimp or anything, but it hurts! So why not wear a guard? They look cool and give you a chance to show off some personal craftsmanship.
Besides, admit it, we're still kids playing mind games and taking ourselves back in time. Robin Hood (Errol Flynn) wore a guard... Howard wore a guard (even had one built into the sleeve of his buckskin shirt!). Heck, a trad longbow archer (real longbow, that is) without a guard would be like Roy Rogers with his six gun stuck in his waistband instead of in a tooled leather holster!