In Gmail, when your bin is empty you get this message:
No conversations in the Bin. Who needs to delete when you have so much storage?!
...and since I first shifted my mail over to google in about 2007, I've mostly gone along with that.
In a fit of organisational madness the other weekend, I realised why this is a rubbish idea.
Mailshots. "look we have a sale! daily deals! come and spend all your money!". Five year's worth of them. And as exciting as it is to be able to see what ebay were trying to tempt me with in April 2009, I don't really think I need to hang onto it - especially when a lot of it is crap from mailing lists I unsubscribed from a long time ago.
Reminder emails from Google Calendar also deserve an honourable mention here.
Removing nearly 10 thousand emails took longer than I'd like to admit. I've also tidied up my filters - so more stuff actually gets labelled on the way in (thus much easier to find and purge at a later date).
What would be nice is a "delete mail labelled $foo after $x days" feature, but sadly that doesn't seem to exist.