This is not only useful, it is a golden opportunity to propose change and get it implemented in order to pass the audit. It is very rare to have such an opportunity when change proposals are going to be looked on so favorably.
Further, it educates the employees doing the internal audit about the internal controls etc. that are part of a good financial structure. By doing the internal audit, assuming you do it well and not treat it as a joke, the people doing the auditing will have a chance to look at the details of what is happening with their systems and to get very knowledgable about the Generally Accepted Accounting Principles (GAAP) that the audit will likely be based on.
One of the most critical things that they may learn is about the importance of internal controls to prevent fraud. It is especially important if the people who are being audited are not professional accountants themselves and thus may not really understand the details of the GAAP.
In smaller companies I have seen many places where the people who set up the orginal systems had no concept of internal controls and thus their systems would have been ridiculously easy to steal from. (I should point out that I used to work for a government audit agency so I tend to notice this stuff even though my job no longer includes an auditing component.) Having these people do an internal audit before the financial audit might help them close those gaps before the real auditors show up.
I would suggest that the internal team consists of multiple people and that no one internally audit his or her own direct tasks and that all work is reviewed by multiple people. You might even find some actual fraud that way.
The one caution I might make is that you do not want to be assigned to do this if management just wants to find ways to "creatively" cover up any problems you find especially any illegalities. Always remember that the alternative term for creative accounting is FRAUD. People who help cover up illegal activites can go to jail with the peope who set up the illegalities in the first place.