Because the customer does not match between the revenues and costs, and customers unable to send it every month so the AAP. To save costs, when they are paid at the end of the round is a work in process.
Because the client does not match the income to the cost. And customers can send money every month so the AAP is recognized when it is paid. Then at the end of the round will be adjusted as work in progress. (By the way, Judy came to the conclusion that the AAP).
Due to the recent customers do not match between income and cost. And customers can't send every month, so AAP saves costs when has to pay. And when the end of the round will need to adjust the work between.