If they work for you do them. But I personally think flat and incline gives you all you need. Tricep involvement can be changed by both variations of grip width and by the way the elbows are "tucked" in, out, forward, or back during the lift.
Between flat and incline presses, flies, and dips, I think for a bodybuilder, there is no need for decline. But if YOU see gains by doing them,...... dont stop doing them just because someone else doesn't like them.
Perfect example: I know plenty of big guys that say DB tricep kickbacks are for girls and pusses. Yet I know plenty of other BB'ers that swear by them. So,.. find out what works for you.