How busy are the car parks by their dispatch center? are the cars staying longer because people are working overtime? how many UPS trucks are visiting?
you buy data flow data from ISPs at all tiers, so even though they're encrypted, knowing how much traffic is going to Macy's.com vs JCPenney.com gives you information you can act on.
We know this is being done, because of reports that say Netflix is X% of Internet traffic. The undredacted reports from those same data sources have much more detail. It's also why some apps that don't appear to have any business model are actually quite valuable.