According to the Marketing Cloud Pricing model, each time a visitor accesses a published CloudPage, this visit is counted as an 'impression' and counts as a Super Message (usage fee), similar to sending an email, push notification or SMS message.
I note that Marketing Cloud doesn't insert a persistent cookie on published CloudPages, which begs the question, is an 'impression' counted each time a user agent (web browser) request is made to a page? If so, is there any control to prevent malicious users refreshing the page constantly or making several requests to a page? For example, I could set up a simple client-side script to make 1,000+ requests per hour to a CloudPage and rack up a pretty significant Super Message bill within a few hours for a poor unsuspecting Marketing Cloud account.
Previously, users could monitor their usage from the 3Sixty Portal but this has been sunset and there doesn't appear to be any way to monitor usage, so I'm unable to clarify what the actual behavior is.