At a wedding, the most common thing I see overlooked is the ability of making clear announcements that can be heard clearly at every seat.
Generally speaking, the dance floor needs to be the power center and guests like to be able to back away from that. The problem arrises though that if you design your system that way, when announcements need to be made, they too are centered around the dance floor.
With that design, just cranking things up for announcements means blasting out those in front with the hopes that those in back can hear.
I've found fill speakers that are only used for announcements are the easiest solution to the problem. Now you can speak and are heard in every corner, but the music can stay in the concentrated area where it's wanted.