Lets talk about lower CPM it means lower cost per mille is advantage to an Ad Publishers because of the danger to the advertiser, the CPM will be bought to be under cost of daily value CPC rate campaign (converted to a CPM value).
CPM works best for visual, branding-oriented campaigns, similar to discourse ads like Google AdSense will manufacture the equivalent of $2-10 CPMs per ad unit supported the clickthrough rate — particularly if the content is correctly optimized.
Top Ad Networks Accept Low Traffic Website
Bidding Strategy on How to Implement Tiered PPC
While high CPM advertising campaign bid budget unfortunately this is bad results to an individual advertisers who are planning to bid like on CPM base. Advertiser should pays base CPM at at discount per ad rate.
Best Practice to Increase Adsense CPC Rate
Adsense Best CPM Advertising Cost
Advertisers best opinions is better choose cost per click or pay per click bidding campaign rate. About Cost per impression advertising better choose lower Cpm bid cost then higher CPC bid because advertisers will be selected high premium websites.