Lemme guess, you work for a company once known as Blackwater? lol
In a case like that, I can understand it. But from day to day operations and relations with clients, investors, and prospects, vendors, suppliers, and on and on, not having copies of communications can work against said company as much or more than it can help it.
In a situation like this, I would be highly concerned this has become a policy to get rid of potentially damaging sh!t they know already exists, than it is to prevent avoidable future costs or inconveniences. You'll know in a year, after they've gotten rid of their damaging archives, and they change the policy back again to retain and backup all emails.