This preference controls how CCRQInvoice access the item list from QuickBooks. In most cases you will want to leave this box checked.

When it is checked the program will read (“preload”) all of the items in your item list from the current QuickBooks company file when you select Order Processing. When orders are processed CCRQInvoice must check on the status of the items in the orders, and if the item list is preloaded then this occurs very quickly.
If the box is not checked then CCRQInvoice has to read the information for each item directly from your QuickBooks company file for each invoice, which normally is a much slower process.
Why would you want to un-check this box? If you are working with a single order at a time, the orders have few detail lines, and you have a very large item list, you may find that the “preload” operation delays the program more than having to check on each item directly. If you see a very large delay when you first select Order Processing try unchecking this option.