As far as I know the camera applies the set values of whatever preset you choose. So Sharpness, Contrast, Saturation and Colour Tone amongst other things are set with different values depending on what preset chosen, regardless of the image.
The values are editable if you find the Sharpness in the Portrait picture style is always too much for example, and obviously there is nothing to stop you doing it per picture,

bonk

but if you are shooting Jpegs it's best to try and find the gloabal settings which give the best results most of the time for each of the presets, Portrait, Landscape, Neutral, Faithful, Monochrome etc and save as your edited presets. I think customising the picture style in camera if you are always boosting/reducing the blues in the computer when you've taken pictures in your Landscape picture style, would be better than altering the Jpeg too much post capture. The closer to perfect in camera the better with Jpeg as any edting is destructive to some degree, even if not thankfully visible most of the time.
It is something most (Jpeg only) people don't do often enough imho, either because of not knowing the option is there, being a bit wary of delving into the camera settings, or being a bit apathetic in accepting what the camera sets and fixing it after the fact if needs be.
This is one of the reasons people shoot RAW as they know what the image is, and can apply the settings to suit the picture rather than a blanket range of settings.