Weddings are more serious than 40th / 50th parties etc I find
At a party , the buzz is already there and a lot of times the dance floor fills with people who will dance to anything
But a wedding, it's going to be in the video they'll keep forever, the first dance etc, its all less laid back from a band perspective
Last one I did was quite a serious occasion, first dance "stand by me" twice round on the bass intro, everyone filming, ok easy line, but still more pressure than a birthday party.
For me though, cost alterations is more about how long before you play your set do have to set up the band, 1 hour or 4 etc