Call Studio 11, ActivityLog new tag, what's it for?

I noticed when creating new Studio apps that the "purge" xml tags are now already populated at 100 days but I also noticed a new parameter that is causing me some pain...

What is this one in bold below? 

purge>

<file_count greater_than="100"/>

</purge>

<last_modified_update frequency="1"/>

What I'm noticing is every call that arrives updates the date/time stamp to the current date/time for EVERY activity log file in my ActivityLogs folder.  Since I always use file rotation "by_day" at least I can figure out which logs have which days.  But every log has the same date/time stamp in Windows and it gets updated with every call, not sure how this impacts the purge setting will have to look into that further, hopefully it's just last modified date/time vs. the create date/time being updated.

I read the 11.X docs, can't find it anywhere.

Thanks, Bill Westby.

Parameter <last_modified_update frequency="1"/> was added to fix purge. There was an “last access data and time” issue.

Ok thank you.  While it makes it slightly more difficult I'll find out if purge works after my customer is live for 90 days. Thanks!