We got married in an Orthodox Church and found out last minute that music isn't allowed on church grounds. We hired an awesome Greek pop singer and had a whole tracklist planned for before and after the ceremony, so the whole "vibe" had to change last minute.
Since she couldn't use any backing tracks, the singer performed her whole set without accompaniment. It was awkward at times but her voice was amazingly powerful on its own. We were able to get in a few dances by clapping along to the beat. We just slow danced to her plain vocals. It was an interesting experience and totally not what we planned on but it wasn't totally awful. Weird yes, but not awful.