It depends on what brand you use or what you add to it. Fondant is basically a sugar product. Wilton makes a readily available brand that does not taste very well. Satin Ice and Pettinice have a good flavor. You can also make it out of melted marshamallows and powdered sugar and it tastes pretty good. Another option is to add in white chocolate or flavorings to achieve different tastes.
There is generally a layer of buttercream icing between the fondant and the cake. In my experience, most of my customers peel off the fondant and eat the cake with bc icing. Some people don't like the flavor or the texture (kind of chewy) or both. Either way, it does make a very smooth and pretty cake! HTH