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: 
My understanding is that the convention of RAW+JPEG started early in pro digital photography (like Sports Illustrated at a bowl game) when computers were slower than they are today and RAW file tools more cumbersome to use. The idea would be that Photo Editors would look through the JPEG files to find the shots they needed. They then sent the corresponding RAW files to the technicians who would convert and tone those images. It assumes a multi-person workflow.

That said, a lot of news organizations just used JPEG files -- especially when they had to transmit files on deadline over a land line modem.
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.