Facebook offers cost per thousand impressions (CPM) or cost per click (CPC) advertising campaigns to marketers, but now the details of that system are being changed. The number of clicks received by CPM advertisers will be reduced, in essence reducing the prominence of CPM campaigns compared to CPC campaigns.
As a CPM advertiser, you are indicating to our system that it s more important that your ad is seen by your audience rather than clicked i.e. you have chosen to pay for impressions, not clicks, said a letter sent out by Facebook. If your main objective is to increase awareness of your business with an ad impression, there is no need for action. However, if your most important objective is to drive clicks on your ads, you should change your bids from CPM to CPC.
This change could drastically alter the strategies of marketers on Facebook, with some suggesting this might double the cost of their advertising.
Source: All Facebook
