Always manually--basically, 90% of the time it's just to bring the R and L sliders into the proper out side edges of the main graph features. Very occasionaly I will make a slight change to the middle slider. I always work on a duplicate of the file so that I can switch it off and on to see my visual result.. With the Shadow/highlight, I usually do a duplicate of the duplicate to work on--for the same reasons.

bwtr