To reduce your Cost Per Acquisition, you can retarget those consumers who have the potential to buy the goods and services which you offer to the users. For instance, you advertise for some services that you want to sell to the public. About one lakh online users saw this ad, and out of those, only 100 users installed your app, out of which 40 actually subscribed to your paid services. Now you can retarget the same 60 users for the next time who have not subscribed but have the potential to do so since they have installed your app. By this, you will be able to target only 60 users for the next time and reduce your CPA.