Today, wise people and moral leaders often recommend keeping a diary. Though many of us would like to do a better job of following such advice, we often don't have as much time as we wish to do such. So the question becomes, if someone can't afford the time or cost to record as much history as we would like, why not at least archive e-mails as an easy way to supplement such efforts?
Thankfully, because of the progress of technology, the cost of storing such on a live, searchable hard disk is only pennies. You can store over 1 million 1K e-mail messages in only 1 Gig of disk space. And do you know how fast a search tool can search such if you're looking for something important from long ago, if you didn't throw it away?
Perhaps, instead of recommending that people ruthlessly throw such away, could the advice instead be something more like save most of them in a folder structure in an archive or personal folders file (.pst file on outlook). Then when the folder becomes large, perhaps after one year, start fresh with a new one. If you did something like this every New Year, imagine the value such a set of mail archived files would become many years in the future. There are many times when we've met someone after an extended period of time, and researched an e-mail conversation we shared many years ago, where both parties were very happy to relive and remember such shared history.
Not only would such surely be very valuable to people personally, such surely would be of infinite worth to future generations hundreds of years from now. If you had such an e-mail archive saved on a DVD when you died, perhaps you could ask a surviving member or friend to post such an archive someplace online for a few years in memoriam. That way it would at least get archived in the Internet archive. Then all such could be saved, for all your descendants to have, forever, for free.
Given primitive technology, having such large amounts of this kind of what might now be considered to be garbage, may seem like something not worth doing. But surely in the near future they will have much more intelligent and meaningful search systems that will make all such very digestible and powerfully available to future generations in ways we can't yet imagine today. Even today's search technology can easily find relevant and important information in any archive no matter how large.
Telling people to make a habit of destroying or avoiding keeping otherwise easy to keep history, whether it be Email, or whatever, is a very immoral and short sited piece of advice. It literally robs future generations of something that will surely be priceless to at least some of them. It certainly would be to us.