I use D800E and D4 Quiet Mode in shooting during live performances in Theatre and find it to be quite helpful. It's certainly quieter than non-quiet mode, and I feel is much more discrete. Certainly quieter than my old rattletrap D700
I would think during wedding shooting you achieve some of this benefit also, at least as compared to non-quiet mode. I just tried both side by side and the D4 sounds just a hair louder but that is very informal/anecdotal.
I also tend to time my shooting somewhat by volume coming from my subject. Sometimes I won't shoot at all, but I listen for noise from either the crowd or stage and then can shoot merrily away. You may at least partially benefit from that approach during a ceremony, but I realize is not always something you can do at a wedding!