As has already been mentioned (or at least alluded to), there are various "tiers" of wedding band, as well as different kinds of weddings (and a range of possible expectations from wedding organizers). I've played weddings that were laid back affairs with bands that did not specialize in weddings. These bands were hired to "do what they do", without the expectation of us sounding like a DJ or of having the kinds of set lists that are typically associated with wedding bands. Those gigs generally involved the least amount of preparation time, the least amount of set-up, the least amount of waiting around and the least amount of stress for the bandleader and players. Presentation standards (what the band was wearing, how the stage was set up, etc.) were also lower.
The majority of wedding gigs I've done, however, have been with top-tier wedding bands. The weddings these bands have played involve more preparation, more set-up time, more waiting around on the day of the gig, more stress and much higher expectations regarding performance and presentation. The people these bands play for invariably have a lot of money and they tend to take their selection of band very seriously. I don't know the absolute ins-and-outs of what goes on behind the scenes (as I'm just the bass player) but I do know that the bandleaders usually have to jump through quite a few hoops when making arrangements with the wedding planners and families, and this will often require several in-person meetings.
The band is the last thing a wedding planner wants to have to worry about (they have flower placements, seating plans, scheduling and the caterers to deal with, amongst other things) so it is imperative that the band be as trouble-free as possible and that the bandleader be someone personable who conducts himself well under pressure. Set-up times can be long and the day's schedule can change at the drop of a hat. There can be more waiting around than actual play time and the comfort of the "waiting area" can vary significantly. The band might be treated really well (e.g., we might have access to the same food and drink as the guests) or as mere employees who need to be fed but who aren't worth "the more expensive stuff" (though I will say that I have never felt as if the band was treated as "just the help").
These kinds of gigs are definitely not for everyone but when the right people are involved they can be a lot of fun. The pay is probably not as good as it first appears once you factor in the actual number of hours involved, but to me it beats any number of other jobs I could be doing. Playing weddings has given me the opportunity to experience beautiful locations, play with great people and spend some time in the world of extravagance and excess without having to foot a bill of any kind

I've eaten from incredible dessert buffets, slept in luxurious hotel rooms, and played some fantastic parties - all thanks to wedding gigs. Too bad that's all on hold for the foreseeable future...