Enhanced cost-per-click (ECPC) bidding should be used to:
- A) Optimize bids using converted clicks
- B) Drive engagement with product brand
- C) Bid for a target cost-per-acquisition (CPA)
- D) Increase total impressions
Explanation: ECPC will increase your max CPC bid by up to 30% (after applying any bid adjustments you’ve set) when it sees a good opportunity. It’ll also lower your max CPC by any amount (even more than 30 percent) if it determines a conversion isn’t likely, so you’ll pay less for clicks that convert less. If you choose the conversion bid metric that matters most to you on your conversion settings page, ECPC will focus on either conversions or converted clicks. If you don’t choose one, ECPC will focus on converted clicks.
Read more here: https://support.google.com/adwords/answer/2464964?hl=en