Suppose that some of the PDF documents you work with contain RGB colors. First, you want to print them on a composite output device, such as a laser printer, for proofing purposes. In that case, RGB colors can be handled correctly. But if it needs to be a color correct proof you need the right ICC profiles.
However, you would like to know which PDF documents contain objects in RGB color, because at a later stage, you might want to print these documents on an offset press. You could then use two different Preflight Profiles to preflight these PDF documents: