What is the purpose of 37 CFR 1.57(b)?

The purpose of 37 CFR 1.57(b) is to provide a safeguard for applicants when a page(s) of the specification, or a portion thereof, or a sheet(s) of the drawing(s), or a portion thereof, is inadvertently omitted from an application, such as through a clerical error. It allows inadvertently omitted material to be added to the application by way of a later-filed amendment if the inadvertently omitted portion is completely contained in a prior-filed application for which priority or benefit is claimed, even though there is no explicit incorporation by reference of the prior-filed application.