Fondant is really just a candy that can be rolled out, and certainly is not as fluffy and creamy as buttercream. I had to get myself out of the mindset that fondant replaces buttercream...it does not.
So my way around using fondant is to make sure that cake is moist and torted on a few levels with the most delicious filling, so the lack of buttercream is compensated for.
It really is decorative. I make mine homemade, and some people will eat it it, others will peel it off and eat the cake. It is for beauty.
However, I found a recipe where the fondant just melts in your mouth. You make white chocolate candy clay, and knead it into the marshmallow or homemade fondant . (DO NOT under any circumstances, use wilton.) The fondant becomes smooth and delicious with a great white choc flavor.