There are many reasons to capture images as RAW files rather than JPEG files.
However, it’s important to note that RAW image files require additional work to
achieve the color balance you’re looking for, whereas JPEG files are color-balanced by
the camera for you. JPEG files are also smaller than RAW image files, requiring less
storage space.
The advantages to shooting RAW files are:

• Increased bit depth allows for more color-correction “head room.” The JPEG format is
  limited to 8 bits per color channel. RAW images store 16 bits per channel, with
  12 to 14 bits per channel of color information. Although it may sound confusing, this
  means you can do significantly more color correction without degrading the image
  or introducing color noise. (For more information about bit depth, see “Learning
  About Bit Depth” on page 38.)
• After the RAW file is decoded, you work with the most accurate and basic data
  about an image.
• You control the white balance, color interpolation, and gamma correction aspects
  of the image during post-production rather than when shooting.
• The image file isn’t compressed, as JPEG files are, which means that no image data
  is lost.
• Most cameras are capable of and do shoot color outside the gamut range of JPEG
  (both Adobe RGB 1998 and sRGB), which means color clipping occurs when you
  shoot JPEG files. RAW files preserve the camera’s original image gamut, allowing
  Aperture to make image adjustments that take advantage of the full range of
  captured colors.
• RAW files give you control of noise reduction (luminance and color separation) and
  sharpening after capture. JPEG noise reduction and sharpening are permanently
  applied to the image according to the settings on the camera.