business expense receipts

We are implementing iExpense and are aware that the user creating the expense report can attach copies of their receipts with the expense report. 

Curious to hear from the community members as to their respective business practice with respect to original receipt documents.

-Do users attach copies in iExpense and submit hardcopies to payables?

-Do users only mail harcopies to payables and not attach in iExpense?

-Are their requirements from an auditing compliance perspective that must be met?

Thank you in advance for sharing your business practices.