If a client gives you a budget to spend on banner advertising through well-targeted, high-traffic Web sites, would you put all of the budget into one or two sites, or would you spread it out among several sites?
It seems to me that it would be more effective to double or even triple the impressions on a couple sites rather than spreading out the impressions among several sites.
However, there is a chance the same viewer will see the same ad over and over again...which is good for implanting your message, but on the other hand they may not have a need for that product/service thus resulting in those added impressions being a waste of money.
Therefore, is it more effective to spread the budget among several sites (but less impressions) and potentially reach more unique visitors?