Receipts

For whatever reason, I have a deeply-held belief that it's important to keep copies of receipts. If I were a good person, I'd double-check the receipt against the credit card bill when it shows up. Of course, the problem with this theory is that (a) I'm not religious enough about it for any discrepancy between what I think the statement should say and what it does say to be a problem, (b) I don't actually go through and double-check, and therefore (c) the office is filled with a year's worth of little slips.

Excepting things where you actually care about having a proof-of-purchase, how is having a receipt useful to me? If my gas pump can send my PDA an expense record magically and my PDA can enter it into my accounting software, does the paper receipt matter? What if the Apple Store wants to send my a receipt by email (they do, and it's pretty cool, but I never actually printed it out)? Is there any value beyond just waiting until the credit card statement shows up? Why do I think this anyways?