Boy do I have a major weakness for scarves. I love 'em. If I were still in Southern CA I could definitely justify wearing a scarf or having one handy in the summer because the desert temperatures dip dramatically once the sun goes down.
If you're in a wedding nowadays that tends to mean you're going to be wearing a dress with thin straps or more common a strapless dress. In the cooler months this means you'll be exposed to the elements of cold and wind but in the warmer months this means you'll be exposed to the sun. The last thing you want is to be sunburned in wedding pictures.
Having a thin, longish, light material scarf to wrap around your shoulders might be an interesting option this summer rather than a light sweater, shrug, even a pashmina (which tends to be heavier), or God forbid a taffeta wrap. Scarves are awesome because of the sheer quantity of different colors and patterns available and they're easy to tuck away in a small purse unlike a sweater. All the scarves shown are from Scarves Dot Net which offers a heck of a lot of variety and at great prices. Also, check out their ever growing Knot Library of different ways to wear a scarf.