The primary business objective of advertising for companies such as mine is to build brand awareness, product benefit awareness and brand identity (eg. are you partial to Coke or Pepsi? Nike or Addidas? etc). Doing this will influence your purchase when you next shop for our categories (eg. your next shopping trip to Walmart or Amazon). Note that we are looking to influence a future shopping trip, any "digital conversion" we may get (eg. click thorough to our product page or an online retailer) really is pure gravy from our point of view.
The primary metrics of interest to us therefore are how many people did our impressions reach (people - not cookies or devices), of the ones we did, how many were in our desired target audience and what was our impression frequency to them (at some point, high frequency becomes excessive). We don't even really look at clicks or conversions unless there is a specific interaction based marketing program.
Hope this helps explain how big advertisers look at media.