Just a few reasons for using LAB
Fast and effective colour correction.
Unlike RGB, LAB is a colour space similar to the human eye.
Create images with visual punch. Contrasts colours without effecting the chroma or luminance
Great for sharpening as you can do this without affecting colour pixels and thus increasing noise.
Good for removing colour casts.
Correcting or lessening lens flare.
Correcting lens vignetting
Good for making masks.
Placing a colour on a precise predetermined Pantone colour, which is great for any product photographers.
Customise vibrancy rather than using the blunt tool in Lightroom.
Understand ICC profiles better as it is all based on LAB.
Useful for determining small differences in color or luminance.