Some photos are seriously oversaturated, undersaturated or need just a small saturation adjustment. For such cases you can use the Saturation feature from the Extras tab sheet. The "Red/Orange Cast" setting of the Cast Types feature may eliminate a lot of saturation from photos, but extremely under- or oversaturated photo, you will still have to use the Saturation slider to get a better result.
Saturation Method
The Sat. Method combo box lets you choose between various methods for adjusting saturation. "Normal" is the standard way of adjusting saturation, but it may add artifacts at higher Saturation slider values. "Median" usually doesn't do that. The six last options represent color filters that suppress the saturation of the color they are named after. For example the "Yellow" option keeps yellow objects from being saturated too much.
Saturation Slider
Positive values of the Saturation slider increase saturation whereas negative values reduce saturation. Dragging the slider to the outer left position turns the image to B/W. Together with the Sat. Method combo box this is another way to create B/W variations of your image.
For normal photos saturation increases or decreases between -10 and 10 are sufficient. Beyond -20 and 20 the effect of the Saturation slider get quite extreme. Such high settings are only recommended for photos that have serious saturation problems.