Would it help airlines, if they knew passenger weight before hand? Its known that pilots and technicians calculate the weight of the plane once everything is loaded, then they can decide on how much fuelling etc. needs to be done.

Would it help airlines, if they knew the weight of all the passengers before hand, say at the time of ticket booking. Having that information, would it help them in optimizing the amount of cargo/fuel etc for the flight?
Despite of the "delay" during the check in procedures, it would be safer than the average companies usually use. 
For instance, the latest FAA guidelines on aircraft weight and balance control set individual passenger weight averages at 190-195 pounds for adults and 82 pounds for kids, depending on whether it's summer or winter. (Based on the assumption people wear heavier clothing in winter.) 
I have read an article, and there are more pieces of information.

Airline begins weighing passengers for 'safety'