Logging of IP address to subscriber/device information results in pretty small logs, often a kilobyte or less per subscriber/device over 90 days.
The basic information is useful for at least in the short term (14 days or less) in responding to or acting upon abuse complaints sent to the ISPs abuse email address which is listed against all the IP address blocks it owns. (example of registration information for one of Teksavvy's IP Addr blocks: »
whois.domaintools.com/24 ··· 12.186.0). To ignore such messages risks getting address blocks or addresses added to various block lists.
Live monitoring of customer's activity seems worse to me than letting the traffic pass as is and responding to complaints.