It is hard to know what to pay for a click or impression. Advertising to countries like the United States and Japan costs more than clicks from countries like Somalia and Cambodia. Is it better to buy more clicks at a low price or better clicks for more money? There is no clear answer to this questions; it depends on the situation of the business.
Can your business deliver goods and services to customers who are far away?
A butcher in Thailand would not do well advertising in the United States. The logistics of sending meat through the postal system make it nearly impossible to deliver a usable product halfway around the world. The expensive clicks that come from the United States would be less qualified than the less expensive within Thailand in that situation.
A technology consulting firm in India that helps large corporations develop data management centers would be well suited to advertise in the United States. Consulting work does not have many barriers. It is not be difficult to deliver this service a long distances; it makes sense to advertise this company in countries across the globe.
How expensive is the product?
Advertising to people who can afford your product is essential. The Indian technology company would be well suited to advertise in places where the management of large corporations reside. These clicks might be expensive but the company can be assured that the people who see those ads are in a position to make important decisions within a company. This same company would not do well advertising into a middle or working class areas because very few people would have the money to buy their products.
A company that sells three dollar earbuds can advertise to a much broader cross section of the population. Earbuds can be purchased by many more people than the services of the technology consulting company.
Do people need your product in this location?
It would not make sense for a Nordic company that produces saunas to advertise in West Africa. The climate is already hot and humid. Conversely, a company that produces lawnmowers would not do well advertising into Alaska. The climate of the frozen tundra is too cold and dry to worry about grass.