We often don’t really notice the music playing, but if the wedding video was completely silent we would want to know what is wrong! Music is part of the video, though it should complement the images and never distract from them.
Always look to the married couple when considering the music. If they give you a list then that is a good starting point, but there is a chance the list is just their favourite songs in general, not a good choice for the wedding video. It is an indication, however. If they give you a long enough list there will probably be a few appropriate songs. Wedding videos often only need two.
Using a song that was popular with the crowd on the night is a reasonably safe bet, provided that it also suits the wedding footage. A dance number might well work with footage of the reception, but probably not with the ceremony.
Soundtracks are usually made to suit the film, but films are occasionally edited to suit the music. There is no hard and fast rule, except that the two must fit together. If you have a lot of ‘B-roll’ shots that work in isolation but not as a narrative you can sometimes make them fit together as a collage. This tends to look a little more like a preview than a story, but it can work well in moderation.
Occasionally you might add music to a background with other audio. Speeches might be best with complete silence, or you might have several highlights of several different speeches linked by some music behind them. I strongly lean towards instrumentals here, but there is probably a counter example somewhere.
Copyright Wedding Video Music.
Of course copyright on the music will almost always be an issue, and you can be fined if the video is ever shown online. Either license the music or go to sites like PremiumBeat that lets you pay once for all the music you will need. Otherwise, you might find you bride isn’t able to share the day’s video with anybody.