To the most useful controls for facial composite:
Facial composite is always an approach to come as close to face as possible, so the controls regarding the overall shape are the most important. Its nearly impossible to get a result that is exactly the same as the real person.
Detail texture is very important to achieve a realistic looking face.
Next very important sliders are Male/Female, Age (could be a little more in both directions), and extremly useful Race Morphing to achieve ethnic differences. I noticed that South Asian is perfect for creating people from south east europe.
Next very useful are the sliders from the shape tab to define the details of the shape as well as the sliders from the Colour Tab.
Genetic is very useful to create similar looking faces, to let the witness decide which is closer to the real person.
Last very useful is the Morph Tab to quickly create the needed expression.
Eyes are always a problem because they are really hard to adjust without distorting them in an unnatural way. So I paint them most of the time from scratch in photoshop to get a realistic look.
Hope that helps you a little bit.
Best regards,
Peter