Question: DSLRs often have the ability to store both a JPEG and a raw file.

Given that the [primary benefit of in-camera JPEG over raw](https://photo.stackexchange.com/questions/15/what-are-the-pros-and-cons-when-shooting-in-raw-vs-jpeg/115#115) is the smaller filesize, and that JPEG+raw is going to store even more data than raw alone, it seems like you're just wasting space on your card and [making your workflow more complicated](https://photo.stackexchange.com/q/4453/378) if you store both.

Why bother storing both JPEG and raw in camera, instead of just a raw file?

Answer: 
I shoot JPEG + RAW when I use my older cameras with bad displays such as the 1Ds mk II. The display of that camera is almost useless (but the image quality is great) and I need another way of quickly confirm that focus is correct etc. I use a WiFi enabled memory card to transfer the JPEG:s to my tablet for quick review and then I import the RAW files to my computer for editing.
I don't know the actual reason for JPEG/RAW mode, but it's the mode I use most of the time.

Occasionally somebody asks me for a particular photo, and it's easier, faster, and more convenient to give them the JPEG than to load it on my laptop and edit in LightRoom or Capture One.

RAW + JPEG is also nice because sometimes the out of camera JPEG is "good enough," though I'll usually tweak it a bit anyway :-)

It can also be nice to compare how I've processed the file versus how my camera saved it as JPEG. Capture One and LightRoom support for my camera (Fujifilm X-Pro1) isn't great, and the camera's built in presets (Velvia, Standard, ...) aren't select-able in the apps, like they are for some cameras. Having the camera's JPEG along with the RAW lets me compare what I saw on the camera's screen with what I've done in the RAW processor.