It will be cheaper. A fondant cake is crumb-coated in buttercream, chilled and covered in rolled sugarpaste, which then has to be smoothed and decorated with, say, sugar flowers - all hand-modelled from expensive flower paste, wired, dried and finished with paint or petal dust. A buttercream cake is also crumb-coated and chilled, but then frosted with a palette knife and, once scraped smooth, the decoration can be piped on pretty much straight away. The whole process is way quicker, which is why it’s cheaper. Also buttercream cake makers are all super nice and will never overcharge.
It will taste better. Cheffing at weddings in historical times, I noticed that after service, the cake plates were returned to the kitchen loaded with uneaten fondant from the wedding cake. Literally no-one eats that stuff. Buttercream is delicious. If you think American buttercream is too sweet, there’s Swiss meringue buttercream, and if Swiss meringue buttercream is too buttery, there’s French meringue buttercream. Or if that’s too rich, Italian meringue buttercream. People who don’t like buttercream are weird and you dont want them at your wedding. They probably don’t like puppies or holidays either.
You can eat all of it. Unless your buttercream wedding cake is dressed with fresh flowers, or some daft topper made out of clothes pegs or something, you can eat your whole cake. Sugar flowers are rock hard and you can’t eat them. They’re for putting in the box that someone gave you a coffee grinder in and stashing in the loft for you to discover and moon over when you pack to go into an old-people’s home.
It will look fun. Even the most elaborately-piped buttercream confections have bags of character and never look boring. Piping is high-risk - once you’ve made a mark it’s not coming off - there’s nothing cautious or tentative about it, which is why buttercream cakes have a spirited style about them that you couldn’t achieve with fondant.
It’s like well trendy. ALL the good cakes are buttercream. For example, Harry and Meghan, Elvis and Priscilla, Tom Daley and Dustin Lance have all chosen buttercream cakes for their big day. Say no more.