I agree about the impressions point. High CTR or not, the Ad is indeed shown to the user, and to look it form a totally different PoV, the low CTR ads mean rela

I agree about the impressions point. High CTR or not, the Ad is indeed shown to the user, and to look it form a totally different PoV, the low CTR ads mean relatively low CPMs (i.e. eCPM, assuming CPC to be low). If looked from a pure branding or impression perspective, this might be desirable (although I'm not saying low CTR is good for the publisher OR the advertiser).