For webmasters with a large number of small websites, we create common campaigns. As a rule, for each creative type we add a campaign with targeting by operating system. The reason why we do this is simple: prices for each OS will vary widely. So, during different moments of time, different ad networks will buy a given OS with more or less profit for you, which allows our system to bring you more profit.
The second model is used for large websites. We add individual campaigns and zones for each website. The reason is that ad networks usually have their own conditions for large websites. Secondly, each website has it’s own traffic “fingerprint”, for example visitor country, devices and uniqueness ratio. So there is much opportunity for optimization.