Which of these metrics is especially important to clients who are running a branding campaign?
Clickthrough rate (CTR)
Average cost-per-click (avg. CPC)
Phone call conversions
Impressions are important to track in any campaign, no matter what your goals are. But they can be especially important in branding campaigns, because they represent how many customers actually laid eyes on your ad. You might not care whether they ended up buying anything from your site, but you do want them to remember that catchy new slogan you paid big bucks to develop and share with the world.
Read more here: https://support.google.com/adwords/answer/1722064?hl=en