Hi Cathy! Because the sour cream is light, it would affect the amount of fat and therefore the richness of final cake. The sour cream itself will lend a bit of extra tang to the cake as well. As for the sugar, the finer the granule the more smooth the emulsion/mix and final texture of the cake will be. If you use coarser sugar, it can sometimes result in a lumpier batter which may not rise as high or have as soft of a crumb. Happy baking!

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