Only time you run Lc and Lm is if you're doing more photographic work where light gradients are more important.
Other than that, there's 0 benefit.
it is still CMYK so you will not expand your colour gamut (will not get more colour)
It will cost more as you'll use (very round figures) 100% Lm for printing 50% M where if running 2x CMYK, you'll only use 50% M.
but...
you don't get more colors, maybe
there are basically 3 ways to achieve the "difficult" light cyan & magenta colors
light cyan & magenta inks
printing them with fewer dots (more white space between them [grainy appearance])
the ability to print different dot size with an algorithm (like mutoh intelligent interleaving)
fools the eye, you don't see graininess (achieving a better presentation of those colors)
kind of like the difference between kodachrome and ektachrome or agfa transparencies for those of us
into photography 50 years ago. you could make the argument then, as well that both printed the same range of colors...