It really depends on platform. Adwords/FB are PPC. But many of the smaller alternate display networks charge by CPM (1000 views) or similar.
As a rule of thumb paying for views means lower value. Often networks try and justify it and say we are as 'premium network'. I treat those words as a red flag more than CPM as I'm yet to test a 'premium network' that has better ROI or customers than others. All that said, sometimes CPM can strike gold if you know what/where/who to buy, but if your taking sales pitches from reps its more often not good.
But sometimes your company is pushing for growth, you've maxed out the performing channels and you have to go for the low or negative ROI sources to reach total targets and when all things are merged metrics work out for the business.
Public Service Announcement: Most FB ads are charged on a CPM basis. Note that they are optimised and often measured on a PPC basis, but they are not charged that way.
As a rule of thumb paying for views means lower value. Often networks try and justify it and say we are as 'premium network'. I treat those words as a red flag more than CPM as I'm yet to test a 'premium network' that has better ROI or customers than others. All that said, sometimes CPM can strike gold if you know what/where/who to buy, but if your taking sales pitches from reps its more often not good.
But sometimes your company is pushing for growth, you've maxed out the performing channels and you have to go for the low or negative ROI sources to reach total targets and when all things are merged metrics work out for the business.