In the staff client today, if a user has 200 items on loan and wants to renew them all, 200 Ajax requests are fired off to the server. If you are a bit paranoid about DOS attacks, you might have safeguards in place that kills off a number of those requests. It might be better all around to have a "Renew all" button that fires off *one* request to the server and gets the total results of the renew process back.