Sour cream is used in baking things such as cakes to help add moisture to the cake or other baked goods.
The sour cream not only adds moisture to the baked goods such as the cake but also the sour cream helps keep the batter thick and makes the cake or other baked goods creamy.
Adding fat content which sour cream has helps make the cake or other baked goods creamier and richer in taste as well.
The sour cream also activates the baking soda in the baked goods and also controls the browning of the baked goods.
The sour cream is able to do all that because of the sour cream being high in fat content & acidity.