Taso, if a client asks for me to so this, I have no idea what area the guests are from or what perspective they have. I only know what my client wanted.
I straight up ask them during my walkthrough.
"Tell me about your families"
--This gives me an idea of any "behind closed doors" battles that may be going on and clues me into anyone who may try to order me around and take over the show that I probably shouldn't listen to. This also helps me gauge any sensitivities to watch out for and work through - death, divorce, step parents, mismatched last names etc.
"Do you have a lot of people coming in from far away"
--While this doesn't tell me much, it gives me a little information to help frame a few things. Not only might these people come up to me and question the way I am doing something (for example on the coasts dance sets begin during dinner which is rare in the Midwest); but it also helps me be sensitive to those who may want some extra time to talk to the bride and groom, perhaps they have an early flight out the next day and I should get their requests out early etc. Again, this question doesn't do much, but it is just more information I can use as I plan. In a few weeks, I will be performing at a large wedding where the couple has relatives flying in from Italy. Having this information helped us plan a special blessing in Italian and incorporate some music from the home country. I wouldn't know if I didn't ask.
"Now, let's talk about your guests"
--Get as much demographic info as possible without sounding discriminatory or creepy. Let's face it, the average age, gender and ethnicity of your audience can affect your play style. Knowledge is power here. You can also broach this from a musical perspective "what did you listen to growing up?", "what kinds of music do your friends like" etc. These types of questions allow you to personalize your performance for the couple and their guests as well as make sure things are appropriate for your audience as a whole.
"Ok, let's manage a few expectations"
--After I've done my fact finding this is where I try to sell the couple on playing to everyone (with an emphasis on the older and younger crows who might leave early) out of the gate and then saving their "Must Plays" of "Marilyn Manson" and "Coolio" for the end of the night in what I call an "Anything goes all request hour" when the crowd in my experience might be whittled down to a handful of drunken friends and family.
Of course this is not the norm and not one size or form fits all, but the theme is knowledge is power - hopefully you get the idea. Questions like these might also help you assess if doing something like trivia etc. would be warranted, and if so, what might appeal to the masses.