Are billboards beneficial for the economy? Why? Billboards cost money to make and don't really seem to significantly benefit anyone other than billboard-makers. A company c putting up billboards presumably increases profits from the resulting increased number of customers, but don't competing businesses' billboards decrease c’s profits by decreasing its number of customers? I don’t see why the total amount of consumption would change, so wouldn't the total amount of business remain roughly constant? So, are billboards economically beneficial or not? Why?
While advertising can be zero sum, here are two additional dimensions you might want to consider. 

Billboards, like other forms of advertising, can inform. In this way Ford can talk about their new 8 seat minivan while GM talks about the more fuel efficient engine of their latest model. This can result in happier customers who value their product better and are willing to pay higher prices for this more ideal product. 

Billboards, in ways not paralleled by other most other forms of advertising, have a negative externality akin to pollution. When the NY Times decides to increase their number of advertisements slightly they bear the costs in customer unhappiness, giving them an incentive to adjust until the private costs and benefits of a marginal ad are equated. But not so with the billboard. The billboard is typically adjacent to public space, so if a nasty billboard ruins the scenery or obscures another billboard the billboard owner doesn't internalize those costs. Since the private benefits of ad revenue continue to accrue to the owner, this leads to too many billboards even if some level of billboard production would be socially desirable.