"any time you rely on humans/users to do something it never works"
On that point, I have to agree.
I cannot count the number of companies I worked in or consulted to who struggle to get users to archive mail. The mailbox is the number one critical application in many companies, and network disk sizes are always on the verge of overflowing.
In order to get things under control, often the only solution is to arbitrarily impose a cutoff date and archive anything older than that. Then you get grumbling in the ranks, although curiously most of the time the impact on actual work is minimal.