When I tell you that choosing your lens makes a big difference and changes your photo drastically you’ll probably: „Duh!! Of course! That’s why I spent so much money on all that glass.“
What we call the „perspective“ is the relation between your foreground (e.g. the wedding couple) and an object in the background (blossoming tree). By using a high focal length you actually compress the distance between the foreground and the background. In that way the tree in the background looks much closer than it actually is, when using 200mm for example. At the same time your wedding couple will look more compressed (or flat) themselves. In fact: the whole picture is quite flat. However when using the „normal“ focal length of 50mm you will get a photograph that looks rather vivid, almost 3-dimensional. That is because the features in your couples face are „less compressed“. It also changes the subjective distance to the background. But since you can kindly ask them to stand a bit closer to your desired background that is not really important.
It probably gets even clearer when you compare the following photos. I placed the wedding couple in front of the mill where they just got married in. Jasmin, the bride, is pregnant and looks absolutely gorgeous in her dress.
I wanted the photos to be comparable, so I composed every photo in a way that the couple would fill the whole frame. In order to achieve that I(!) had to move. The couple stood in the same position the whole time. I started with 17mm. Here I had to be super close to them, in order to fill the frame. The last photograph is shot with 200mm. At that point my distance was roughly 10m.
The longer the focal length the closer the couple appears to be to the mill.
Once again: neither the couple nor the mill ;) moved in any of the shots. Only me and my tripod did. Note how the proportions of the couple changes as well.
Note as well how different each photograph looks with the different lenses. Some (like the 17-40 zoom) look rather dull and lack contrast, whereas others like the 50mm Sigma Art creates a rather luminous image. That of course also has to do with the sun. On the wide angle shot the sun is part of the picture which gives you a completely different look. I shot the photos in one go. The light hasn’t changed in that time, yet the photographs look quite different.