Safehand is an Alethi term for a female's left hand. According to Vorin cultural tradition, it is obscene for a woman to leave her safehand uncovered. Upper class (i.e., lighteyed) women adhere to this tradition by wearing a sleeve that covers their left hand loosely. Often the sleeve has a safepouch sewn on its inside for women to store personal objects there. It is considered extremely rude to open another woman's safepouch.
Further, for an Alethi woman to rest her clothed safehand on a man's shoulder is a gesture reserved only for family.
In an interview, Brandon stated that the tradition derives in part from " ... a famous book written by an artist who claimed that true feminine pursuits and arts were those that could be performed with one hand, while masculine arts were those performed with two hands, in a way associating delicacy with women and brute force with men." He has also compared it to traditional foot binding in China. It's a cultural thing rooted in sexism. There isn't any practical reason for it.