For me the benefit is obvious - Since I never call my parents by their names and only address them as dad\mom it's much more natural for me to @dad when I'd like him to see something. In fact, that's how I've stumbled upon this feature. Using FB when very tired and just accidently wrote @dad instead of @<his name>. Indeed it would be awesome if Facebook crowdsourced their road map, that's a great idea.