With most everyone focused on CTR and Avg. CPC, I find it odd that biggest loss, Impr. is not being mourned as it should.
It came to me to later than I feel comfortable admitting, but eventually I realized that Adwords provided much more than traffic alone.
I often started campaigns so they have little chance of getting clicks, but were likely to gain impressions. These campaigns were always highly segmented geographically, by the day of the week, time of the day, etc . . .
With only impression data, I could quickly start to gain a detailed knowledge of demand with little investment other than my time.
Now that the amount of ads per page that don’t get clicks has decreased, it has lengthened the time to acquire the adequate amount of data.
It seems that Google has removed yet another source “free” of data from the webmaster's toolbox. However, you can still obtain a lot while spending very little. For the time being.