Mostly, a brass saddle help lam-topped gutars that are a little muddy-sounding (adds brightness and sustain)...
OTOH, sometimes a brass saddle can add too much brightness, making some guitars a bit shrill.
Inexpensive enough to try, and easily reversed if you don't like how it sounds, though.
+1
Daion Guitars - late '70's / '80's did brass nut and saddle.
They used solid Douglas Fir for their tops on their better models and laminate B/S's
Brass can sound brash / course - dare I say 'metallic', I replaced a brass saddle with bone and the owner, a flatpicker liked the fuller - sweeter tone (his words).