My old boss, (an experienced IT manager who'd worked his way up, so not just a random user) used to basically delete every email unless it represented a current task. If he needed an old email, he'd just go search in the deleted items.
He was most annoyed when I empted his deleted emails without thinking, but had to admit that it was entirely his fault for having such a non-standard workflow.
(and M, if you're reading, sorry, but I'll stop taking the piss when you start using your inbox like a regular person ;)