Shooting JPG vs. Raw: DSLR Know-How with Tamron
He says "cameras can shoot RAW plus JPG. I don't know why they do that, but you could"
There are many reasons to shoot RAW plus JPG
(1) you can capture B&W in the camera and still have the RAW file for full color. This can be very important when learning B&W composition as the image on your LCD will be the JPG and will look B&W. Looking at an image in B&W will definitely help you with your compositions! Even if you ultimately decide to custom process the B&W from the RAW file using a Topaz or Nik plugin you will know what you captured when you are capturing it
(2) Shooting a wedding where they want B&W (and color) images. You do not have to spend endless hours post-processing. If you can get it right in camera then by all means.
(3) Shooting a portrait session where they want B&W images. If you are putting B&W images on your wall and showing your client color images on your LCD there is a disconnect. Many maternity and newborn and child sessions are awesome in B&W and if you are touting your session as a B&W session then you should be showing them the images in B&W
(4) You are just learning about RAW. If you get perfect images THEN you can delete the RAW files back at home and only process those files where the exposure is not dead on.
(5) You are usually dead on with your exposures and don't want to waste time processing RAW files, but want to be 100% that you nailed each image. Let's say you are photographing flowers and a bird or a bear comes along and you have to swing the camera around and you cannot adjust your setting fast enough. If you shot RAW you stand a decent shot of being able to save that image, but if you only shot JPG then if the exposure was not correct then you are out of luck.
I am sure that there are other instances where RAW + JPG is good...