The faced hem is not only functional, but, with a little creativity, it can look beautiful as well.  The purpose of the faced hem is to allow you to save fabric.  It's mainly used for when, for whatever reason, there's not enough fabric for a traditional sized hem or maybe the garment is a little too short and you want to let out the hem as much as possible.  Instead of having a hem that's using an 1 1/4" of fabric, you can get by only using 1/2" and it'll still look nice.  This might not see like a huge difference, but sometimes every little bit counts.  Because you're using a separate fabric to make up some of the hem, you can have a little fun and make your hem facing a contrasting fabric.  Even if you don't use a contrasting fabric, your faced hem will make the inside of your garment look nice and professional.