The one most important thing to remember when playing a wedding gig is,
That despite any plan, things will change.
Set breaks will shift, set lengths will shift, set content will shift.
The bride and groom may be stuck doing photos and the jazz cocktail set may have to run long, they may have gotten there ahead of schedule, and want to get to everything sooner.
There may be a special request from an important member of the audience.
The audience may be dancing hard to particular song, and ending it would kill the vibe, being ready to transition to a similar song with a similar vibe durring a dance set without stopping is vital. Similarly, identifying when the crowd needs a break and a slow song needs to be played (couples skate) is vital.
You should also have at least one sets worth of extra material ready to go -- the moment you don't, the host will offer the band an extra thousand to play another hour.
So, what has your experience been when you have played gigs where the set list is more recommendation than a "Set" list?