Traditional ad blocking is bad, but element hiding is worse. In our example, Facebook will record the impression, but J Crew’s reporting system will not, leading to volume disputes between the companies. Without a record of the impression, J Crew’s performance measurement systems will also be unable to record any advertising success metrics like viewability, ad engagement, and post-impression sales. Facebook’s performance will appear weak. And depending on contractual terms between the two companies, J Crew may even be responsible for paying Facebook for this hidden impression. Through no fault of either company, their business relationship may be damaged.