|A lined pocket flap is less bulky and can be more precisely sewn and pressed than a pocket flap that is self-faced. I'm always interested in increasing the accuracy and precision of my sewing and this is a nice touch that helps me do that.
I have prepared a photo tutorial (accessible at the photo link above) to show how it's done. The tutorial covers accurate stitching, trimming, pressing and topstitching. There are detailed captions under each photo which will give you more information.
Ask questions in the comments section, if you have any.