When Time pictured an underwear-clad pop star on its cover, hailing her as one of the world’s most influential people, it looked like a crass sales ploy. But in Beyoncé Knowles-Carter, they had more of a point than they seemed to realise. Time had asked Sheryl Sandberg, the head of Facebook, to praise the singer for joining various do-gooding campaigns — but this is the least of her achievements.