I use cake mixes for my cakes. I usually use the pound cake recipe on the side panel of the DH Yellow cake mix box...one box mix, 4 eggs, 1 pkg. pudding, 1/3 cup veg. oil, and 1 cup water.
I have noticed that other recipes call for sour cream. What does this add to a recipe???
I use sour cream in all my cakes; it gives the mix more of a "from scratch taste" and makes it moistier.
I'm a realtive newbie but I have used sour cream in mine and they turn out really moist and dense. I have tried the durable cake mix and cake extender recipes on this site and both are really good. 
Just watch out that you don't add in too much sour cream or the cake will be almost wet.
I've had very good luck with the Super Enhanced Cake Mix Recipe (http://www.cakecentral.com/cake_recipe-1953-1-Super-Enhanced-Cake-Formula.html) that uses sour cream. It turns out a moist, dense (but not soggy), fabulous-tasting cake that really disguises the "mix" flavor. I also add a package of instant pudding/dream whip (for white cakes), an extra egg, and usually 1/4 - 1/2 teas of almond extract. I may never go back to scratch cakes again!
The sour cream (along with the other "extra" ingredients) makes the cake moister, gives it a better texture, and improves the flavor.
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