Canon Picture Styles; Auto, Standard, Portrait, Landscape and Fine Detail are all for producing out of camera JPEGs. Picture Styles neutral and faithful are provided to use as the starting point for RAW adjustment. Of course the other JPEG Picture Styles can be converted to neutral or faithful when the image is imported into DPP. The 1Dx II user manual describes neutral as 'suited for processing the image with a computer [that is, RAW adjustment]. For natural colours and subdued images with modest brightness and colour saturation.' The manuals for other models and the DPP user manual say something similar.
For what it's worth, I use neutral Picture Style with saturation = 0 in DPP for most images. Only rarely do I use the global saturation adjustment available in DPP. However, once I have a 16-bit TIFF version of the image in Photoshop, I quite often apply a little local saturation adjustment, either more or less saturation. I usually apply more saturation to critical parts of the bird when the image was recorded with a high ISO. High ISO images have less colour dynamic range and can look a bit subdued, even washed out. The amount of saturation I apply is usually less than 10 points in Photoshop, this is barely noticeable. I usually apply the saturation in one colour channel only otherwise I use the the RGB option if I want to boost the overall saturation. I mentioned the possibility of applying less saturation and this is something I find useful if there is a brightly coloured distraction in the background. Again, this is a local adjustment confined to the offending object. I sometimes use less saturation in one colour channel when there is a colour cast on part of the bird due to a reflection of light from the environment, for example, the top side of a bird in flight might have a blue cast due to sky reflection or the under side of a seabird in flight may have a blue-green cast due to light reflected up off the water.