Flat top is required when you required to decorate it with ganache or whipping cream. In that way there is no need to trim down the cake and waste a pert of the delicious cake. However, if you follow the recipe as is, then surely it helps to get the flat top after baking. Another way to get flat top is, put some ice cubes on a tray and keep it in the lower rack in the oven. Having said that, I personally have not tried this as of now. But do share the feedback if you try it.