it seems we are back to semantics once again (my favorite thing!!!!!)
what is a desk audit, one done at a desk obviously ...... LOL
But to me it is part of the prepration for the audit as well..the plan, putting the scope on paper, checklist prep, familiarization with the system and department and the requirements (scope?), understanding the who why and how of what you will be looking at, time schedule insight, efficiency tool...UMMMMMMMMMMMMM how many more ways can I say the same thing with slight variations???????????????
The registrars need to know that the system , on paper, meets the standard.....as in when the standard says "thou shall" you say "We do" and check for that before they come in,,,why? So as not to waste time if there is a gaping hole, or an element is missing from your system. And for many of the same reasons stated in my triad above.
Should you do one before being audited? Well, it is my belief that when you are to be audited, you need to go anywhere they plan to and be one step ahead.... just as good practice, But that is just my humble opinion and certainly not a requiremnet