I think with regard to the origins of the requirement, you have to trace back to a private member's bill. It wasn't the private member's bill that was enacted ultimately but in fact something the government put forward.
In terms of the why and what it does, it is meant to serve parliamentarians primarily. It's not primarily a management tool; managers already have that kind of information. It's not primarily an audit tool because the quarterly financial statements aren't audited and the auditors would have full access to all information at year-end. So it is truly meant to be a tool for parliamentarians to help them monitor in-year spending and results.