Coaches can't get enough athletes. The more a player can do, the more valuable he is. In every recruiting class, there are prep football players who display the versatility to contribute in a number of ways at multiple positions, and coaches must decide what position they should focus on once they arrive on campus.
When it comes to skill position players (QB, WR, DB, RB, etc.) who are candidates to play multiple positions, ball skills, speed and fluid movements are key components. All three of those traits are "must haves" at cornerback and wide receiver. The main reason players with great speed and moves end up on defense is because they lack the hands and ball skills to play offense.
Most importantly, the one characteristic that all great athletes have is football instincts. A natural feel for the game can often compensate for a lack of physical prowess in one area or another. Instinctively knowing what to do or how to play or where to be is something that can sometimes be overlooked when scouts and coaches become enamored with physical tools. When you combine the physical tools with instincts, you have a natural football player or "athlete."