A Raw file is…
- the complete (lossless) data from the camera’s sensor.
Several of those points are important, but this is really at the top of the list.
This is why a RAW file is referred to as the closest thing to a "digital negative", containing every bit of information the camera saw. In turn, this is what allows such extensive editing control, namely over elements like the exposure, color temperature, highlights/shadows, and color accuracy.
In short, JPEGs are fine if you simply want to take snapshots; RAW is preferred if you want the power to capture and process high-quality images.
Personally, I shoot everything in RAW because it provides a bit of a 'safety net' when editing, something that would be considerably more difficult if working with JPEGs.