The Pontiac algorithm will optimize the campaign based on the selected KPI.

• CTR (Click Through Rate): Select this KPI if you are trying to increase the number of clicks and overall traffic through a site. This is calculated by dividing the number of clicks by the total number of impressions.
• CPA (Cost Per Acquisition): Select this KPI if you are trying to decrease the cost per conversion on the campaign. This is calculated by dividing the cost of the campaign by the number of conversions.
• vCTR (Viewable Click Through Rate): Select this KPI to increase the number of clicks on viewable ads. This is calculated by dividing the number of clicks by the total number of VIEWABLE impressions.
• Viewability: Select this KPI to maximize the viewability of your campaign. Per IAB guidelines, an ad is considered Viewable if 50% of the pixels are in-view for 1 second or more. This is calculated by dividing the number of viewable impressions by total impressions served.
• VCR (Video Completion Rate): Select this KPI for video campaigns. This is calculated by dividing the number of video completions by the total number of videos served.
• Reach: This KPI will attempt to spend the entire allocated budget without optimizing to a performance metric

For KPI recommendations by Product see here:

Product Offerings & Targeting Strategies.