Yes, color adjust is extremely useful; I use it all the time, especially to soften or harden masks, or (partly) change colors. Like when you have a beach and want to make wet sand; set upper limit in a surface shader, add a color adjust as child and set gamma to 0.8 or so, add a (no-RT, or sometimes RT) reflective shader between those et voila, wet sand. You can also mask a surface shader (+ color adjust) by a XZ stretched PF to darken part of a rock wall into strata layers.