(Result of much discussion today on #duraspace)
Currently, usage events can be recovered from dspace.log, but that file is (w.r.t. statistics) cluttered with many other types of records, and the format is not the best for statistical purposes.
Usage event data have a much longer useful life than most of the other records in dspace.log. That is problematic for long-term storage of event data.
This feature would write simple flat records of usage events only, in a format suitable for processing by statistical tools, web log analysis tools, and the like, to a separate file, much as e.g. Apache HTTPD can write separate access and error logs.