A wedding without music is a sad wedding, no matter the wedding type.
But you should be very careful in choosing the music.
First off, I should point out that by “music” I mean live music. Therefore, you should choose the genre very carefully or maybe get the help of someone knowledgeable. A wedding planner, for one, will know with certainty how to best meet the couple’s requests on this matter as well.

Let’s distinguish among the various moments of the ceremony, as the music cannot be always the same. So, we should know what to do for the religious moment (if any), for the City Hall moment (if any), and finally for the reception moment. This last one, furthermore, will have to be separated into parts, as what we listen to during the cocktail, for example, is not appropriate for the cake cutting, and vice versa.
Now, an important consideration before everything else: if the couple decided for a classic ceremony (or, in any case, something upscale), they’d have to recruit musicians able to play stuff ranging from Mendelssohn’s wedding march to a delicate Bach adagio. If the venue allows it, an organ with a harp and some violins would be perfect.

The music for the religious ceremony should never start before the wedding march, therefore, no musical entertainment should be heard prior to the bride’s appearance and her walking down the aisle to the altar (or anything else along these lines). The guests won’t be there for a cocktail or a vernissage, so they will know that music will start only at the very beginning of the rite.
Additionally, a dedicated person, ready to let the musicians know when to start playing, will be there.

Lately, some warmup by the musicians before starting to play has been well received. So, just a few notes here and there that will sound like the musicians are getting ready, so to speak, are kind of normal to hear before the real thing starts kicking in. It might sound nice and let people think of something romantic.
If strings have been played in church, they could then continue during the cocktail until the wedding banquet, when they will diversify their repertoire according to the different parts of the lunch or dinner. They will have to move, therefore, to position themselves in another area, where they will continue with some more festive tunes: a radical change from the sacred music played during the religious ceremony (if any). Here, though, I would recommend continuing with some classical tunes: Vivaldi’s Four Seasons, for example, is always very appropriate and appreciated.

The music background during the seated lunch (if any) should always be very delicate: a piano or, again, some strings would be the best choice. The chosen tunes will have to follow a pattern and be in line with what played during the prior parts of the wedding, bearing in mind that the guests will be more and more tired as time goes by, so, nothing loud but, at the same time, nothing sleepy (!).
Between the end of the lunch and the cake cutting, it might very well be that guests have to change position: they might have to move to a different part of the garden, if the wedding takes place in a historical mansion, like the one I wrote about some Sundays ago (remember?), so the musicians will have to move as well. For the cake cutting, it would be neat to hear a festive and joyful tune.

Finally, in case of an evening wedding, if the newlyweds planned to have dances, then the strings will have to be replaced by a keyboard or, maybe, a good dj (one of the “calm” ones). In a wedding I went to some time ago, for example, this dancing part was organized by hiring a fantastic band that played 1980s pop music with saxophones and trumpets. I remember that wedding as a success; everyone was so happy and had a lot of fun. And the bride showed off her second dress… but we’ll talk about that some other, appropriate, time.

An important recommendation is not to let personal tastes prevail too much. If, for example, the newlyweds are great fans of a type of music that’s not really appropriate for any of the situations described above, they should find a way not to indulge that music taste.
I would suggest you browse stuff on youtube for a while before making definitive choices.
Until next Sunday