butter cream is beaten up with butter and icing sugar much sweeter than whipped cream whipped cream is much nicer in sponge cakes and you could have a chocolate fudge frosting on top of a chocolate cake with the whipped cream in the centre . boiled white frosting and royal icing is more for special occassion cakes such as a Xmas or wedding fruit cake where you might want to decorate the top after the plain icing is smoothed on. I buy my icing in the super markets when making xmas or wedding cakes which come in a block and you then roll it out to the size of your cake. here in Australia it's called orchard icing