When choosing the file format to shoot on your camera, there is no other way to go than RAW files.
Yes, it's tempting to just use the JPG file format we're all familiar with. But JPG files compress pixel information from its original (RAW) state. RAW files take up a lot more space on your memory card, but the things you can do with them are magic.
Take a look at this shot of a father-daughter dance from a recent wedding. I had turned my flash off a minute or two earlier, and forgot to flip it back on before shooting into the sun. The result of such a mistake is a totally unusable photo.
Unless you shot it in RAW.
Salvaging something this nice is totally impossible with JPG files. Look at how much information was preserved, even in the darkest parts of the photo. I pushed the capabilities of RAW editing to its limits to end up with this shot, so there is naturally a little grain in the shadows, but who cares?? It's a fantastic moment that would otherwise be lost forever. (And I promise, your clients don't care about that grain as much as you do.)