A custom die can be nice in a couple regards. Most of them will incorporate a bushing to size necks in accordance to your neck, turning thickness, and tension requirements. After that, in a true BR environment, if cut based off your chamber, it will allow a bump of the shoulder of , say, .001”-.002” to allow proper, easy, chambering and modest sizing of the base of the case giving proper fit but eliminating a harder “ click” on final bolt lift that can occur with some actions, leaving the rest of case unsized.
While gunsmiths often are not enthusiastic about supplying custom FL dies, and as stated others work reasonably well, as you invest in guns, gear, etc., it is great to have your own reamer and a matched FL die for same.
I have four different platforms and several barrels and while I don’t, I can put any case in any barrel to shoot with no more than maybe a click or so on my die adjuster so I don’t have to reinvent the wheel all the time. Not a bad backup plan.