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: 
**In the RAW+JPEG workflow, JPEG is what you shoot for. RAW is the safety net.**

The primary benefit or JPEG is not smaller files (that's the second), it is that **JPEGs are actually images**. Images have advantages over RAW files, already mentioned by others: quick preview, ready to email, no processing required, etc. Once the shot is taken you are done if you did things right.
I've suggested RAW+JPEG to photographers who are fairly new to digital photography and are ambivalent about switching to a raw workflow, because they don't have raw-capable tools or are worried about the effort involved. I point out that they can keep using the JPEGs like they always have, but the raw files will be there, like a digital negative, for whenever they're ready to work with them.