The guys who do comps down here usually trim it off with a fillet knife after cooking and before slicing. I usually leave it on unless it's unusually thick. Sometimes I trim of off when I slice if I see one that's too big. Personally, I like a little fat on my brisket.
BBQ Apprentice - Old Country Brazos offset, 22.5 WSM, Various gassers, portable grills, etc.