you use a subfile to display multiple related records, such as line items on a purchase order. A subfile can only contain 9999 records, so if you have more than that you need to do page-at-a-time (PAAT) subfiling and control populating the screen with the correct next/prior set of data. In reality, no one would want to look through 9999 records, so you would want to do PAAT much sooner. Load-All subfiling is appropriate when they are a relatively few set of records, such as a prompt list of reason codes for why the user wanted to cancel a line item on their purchase order.
Regarding BigKat’s answer, if you allow “position to” on the SFL, PAAT is better because they you can allow Page Up, if the user has positioned past where he wanted to start,