An advertiser using viewable cost–per–thousand impressions (vCPM) bidding wants to maximize exposure on a specific set of sites selected for a new campaign. Which is a best practice when setting up the campaign?
Set bids at the ad group or campaign level
Choose websites that represent a variety of themes
Set bids on individual placements
Create a campaign for each website
If you want to set bids for an individual targeting method in your ad group, you can use custom bids. These are max. CPC (or max. vCPM) bids that you set. If you enable custom bids for placements, for example, you can set max. CPC bids on individual placements that you add.
Get more (or less) traffic from placements by setting individual placement bids:
If you find that advertising on a specific site works well, you may decide to increase your bid for just that one site to be more competitive and increase your potential exposure on that site.
Read more here: https://support.google.com/adwords/answer/2470108?hl=en
Doesn’t restrict your ads to showing for the targeting method you’ve selected
Read more here: https://support.google.com/adwords/answer/1209882?hl=en