Well my girlfriend not only deletes every email and empties the trash in her mailbox daily, she also throws away every piece of paper she receives. This has often led to problems (e.g. wanted to check and see if email again or needed a receipt to exchange something). However she says that those inconveniences are better than having to store all the stuff.

My motivation? I guess deep down a fear of loss, buy also just the good feeling of having stuff ready in case I need it one day.