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 because my camera produces *really good JPEG output*. It has flexible control over tone curves, color, and contrast. I'm not usually interested in producing HDR-compressed images — in fact, I often prefer a high contrast look which reduces dynamic range. If I get the exposure and other settings right, I really don't benefit much from RAW.

If I make a mistake with white balance or am in a tricky situation, I have the RAW file to take advantage of. Most of the time, I develop that in-camera, using the built-in tools to do so, but in the cases where I'm not satisfied with that, I use RawTherapee. (My camera allows adjustment to the color of the LCD; it's not completely color profiled, but it's basically neutral, so I can trust my eye well enough.)

I know that some cameras only allow highly compressed "Basic" JPEG in combination with RAW; mine lets me save JPEGs of any quality, and in fact, I usually use ★★★, only increasing to ★★★★ when the scene needs it or when the image appears particularly special. (See [Is it worth using the Premium JPEG quality setting?](https://photo.stackexchange.com/questions/21690/pentax-k-5-is-it-worth-using-the-premium-jpeg-quality-setting))

And, in fact, in the interest of keeping my lifetime data load sane, I only keep the RAW files for those particularly special images. I know this is verging on sacrilege against the conventional wisdom, but I haven't regretted it yet. If I had *paying customers*, I'd definitely archive it all, just in case.
As a professional photographer I rarely need the jpeg files so I only turn them on when needed. When I do need them it is because I need a fast edit and raw files require a bit more processing time and CPU power than the average laptop can handle.

For instance I went to photograph a luncheon for a company where there was to be a few big name people speaking. When I arrived the contact told me he was told at the last minute that he needed a quick turn around on 5 of the images... a couple hours instead of having the entire shoot ready 6 hours to a day later. I turned on the raw + jpeg so I would have the ability to grab the jpeg quickly and do a quick edit and supply him the file quickly after the event when I got back to the office.

I've also had it where there were times when I could download the disk of images right on site when the client changed the deadline. They could have an untouched file immediately after shooting it, and they wouldn't need Photoshop, Lightroom or whatever program to convert a RAW file into something they could use. 

Speed is the main reason to use Jpeg (size is another one). The reason to use raw is because it gives more latitude for adjustments and a wider color space, although the new jpeg revisions that just came out could make the wider color space a moot point.