There is quite a large cost to that, though. Being able to search through old emails is a lifesaver. I can't count how many times I have searched through email to find some account info I set up years ago, or to get date information about when something happened. Just today, I searched my email for my old FastTrak account info, and found it on an email from 5 years ago.

Deleting all my email would be a big cost to pay for a gain that I can't exactly quantify; I would have to figure out the likelihood of my data being leaked over time and the cost to me if the data was leaked. That isn't readily obvious what the risk factor is for me, but I KNOW the cost factor.