Buttercream, in comparison, to whipped cream, has a creamy and spreadable texture. At the same time, whipped cream is airy and smooth and is not as spreadable as buttercream.
Whipped cream is much lighter and fluffier, making it a poor choice for filling a cake. So buttercream is better for cake fillings as it has a rich and creamy texture. Also, whipped cream is preferred at the top of the cake for piping.