Enhanced cost-per-click (ECPC) bidding should be used to:
Optimize bids using converted clicks
Drive engagement with product brand
Bid for a target cost-per-acquisition (CPA)
ncrease total impressions
Enhanced cost-per-click (ECPC) is a bid strategy that automatically adjusts your manual bids for clicks that seem more likely to lead to a sale or conversion on your website. Unlike Target CPA, which targets the cost per conversion, ECPC uses your max CPC bid to target conversions. Compared with Target CPA, ECPC is constrained by your manual bids, but can still help you optimize for conversion.
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